diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index c6fd88fabd8..70ffd5ef728 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -20,6 +20,10 @@ on:
 permissions:
   contents: read
 
+env:
+  OVERRIDE_FEATURES: 'DEPRECATE_TEMPLATE_ACTION'
+
+
 jobs:
   lint:
     name: Linting
diff --git a/packages/@ember/-internals/deprecations/index.ts b/packages/@ember/-internals/deprecations/index.ts
index 33dc91a155a..c3ed54143fe 100644
--- a/packages/@ember/-internals/deprecations/index.ts
+++ b/packages/@ember/-internals/deprecations/index.ts
@@ -97,6 +97,15 @@ export const DEPRECATIONS = {
     until: '6.0.0',
     url: 'https://deprecations.emberjs.com/v5.x/#toc_deprecate-implicit-route-model',
   }),
+  DEPRECATE_TEMPLATE_ACTION: deprecation({
+    id: 'template-action',
+    url: 'https://deprecations.emberjs.com/id/template-action',
+    until: '6.0.0',
+    for: 'ember-source',
+    since: {
+      available: '5.9.0',
+    },
+  }),
 };
 
 export function deprecateUntil(message: string, deprecation: DeprecationObject) {
diff --git a/packages/@ember/-internals/glimmer/lib/helpers/action.ts b/packages/@ember/-internals/glimmer/lib/helpers/action.ts
index 8f2423972ab..015cea88b24 100644
--- a/packages/@ember/-internals/glimmer/lib/helpers/action.ts
+++ b/packages/@ember/-internals/glimmer/lib/helpers/action.ts
@@ -4,6 +4,7 @@
 import { get } from '@ember/-internals/metal';
 import type { AnyFn } from '@ember/-internals/utility-types';
 import { assert } from '@ember/debug';
+import { DEPRECATIONS, deprecateUntil } from '@ember/-internals/deprecations';
 import { flaggedInstrument } from '@ember/instrumentation';
 import { join } from '@ember/runloop';
 import { DEBUG } from '@glimmer/env';
@@ -278,6 +279,10 @@ export const ACTIONS = new WeakSet();
   @public
 */
 export default internalHelper((args: CapturedArguments): Reference<Function> => {
+  deprecateUntil(
+    `Usage of the \`(action)\` helper is deprecated. Migrate to native functions and function invocation.`,
+    DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION
+  );
   let { named, positional } = args;
   // The first two argument slots are reserved.
   // pos[0] is the context (or `this`)
diff --git a/packages/@ember/-internals/glimmer/lib/modifiers/action.ts b/packages/@ember/-internals/glimmer/lib/modifiers/action.ts
index 249eaeb9436..66da57e79dc 100644
--- a/packages/@ember/-internals/glimmer/lib/modifiers/action.ts
+++ b/packages/@ember/-internals/glimmer/lib/modifiers/action.ts
@@ -1,4 +1,5 @@
 import type { InternalOwner } from '@ember/-internals/owner';
+import { DEPRECATIONS, deprecateUntil } from '@ember/-internals/deprecations';
 import { uuid } from '@ember/-internals/utils';
 import { ActionManager, EventDispatcher, isSimpleClick } from '@ember/-internals/views';
 import { assert } from '@ember/debug';
@@ -204,6 +205,10 @@ class ActionModifierManager implements InternalModifierManager<ActionState, obje
   }
 
   install(actionState: ActionState): void {
+    deprecateUntil(
+      `Usage of the \`{{action}}\` modifier is deprecated. Migrate to native functions and function invocation.`,
+      DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION
+    );
     let { element, actionId, positional } = actionState;
 
     let actionName;
diff --git a/packages/@ember/-internals/glimmer/tests/integration/application/actions-test.js b/packages/@ember/-internals/glimmer/tests/integration/application/actions-test.js
index a0d3df9d997..19397b08b9c 100644
--- a/packages/@ember/-internals/glimmer/tests/integration/application/actions-test.js
+++ b/packages/@ember/-internals/glimmer/tests/integration/application/actions-test.js
@@ -4,6 +4,7 @@ import Controller from '@ember/controller';
 import { getDebugFunction, setDebugFunction } from '@ember/debug';
 
 import { Component } from '../../utils/helpers';
+import { DEPRECATIONS } from '../../../../deprecations';
 
 const originalDebug = getDebugFunction('debug');
 const noop = function () {};
@@ -14,6 +15,11 @@ moduleFor(
     constructor() {
       setDebugFunction('debug', noop);
       super(...arguments);
+
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
     }
 
     teardown() {
@@ -23,7 +29,7 @@ moduleFor(
     ['@test actions in top level template application template target application controller'](
       assert
     ) {
-      assert.expect(1);
+      assert.expect(2);
 
       this.add(
         'controller:application',
@@ -47,7 +53,7 @@ moduleFor(
     }
 
     ['@test actions in nested outlet template target their controller'](assert) {
-      assert.expect(1);
+      assert.expect(2);
 
       this.add(
         'controller:application',
diff --git a/packages/@ember/-internals/glimmer/tests/integration/components/contextual-components-test.js b/packages/@ember/-internals/glimmer/tests/integration/components/contextual-components-test.js
index 074e4e4a5c2..a1e951ed7d9 100644
--- a/packages/@ember/-internals/glimmer/tests/integration/components/contextual-components-test.js
+++ b/packages/@ember/-internals/glimmer/tests/integration/components/contextual-components-test.js
@@ -4,6 +4,7 @@ import { moduleFor, RenderingTestCase, applyMixins, strip, runTask } from 'inter
 import { isEmpty } from '@ember/utils';
 import { A as emberA } from '@ember/array';
 
+import { DEPRECATIONS } from '../../../../deprecations';
 import { Component } from '../../utils/helpers';
 
 moduleFor(
@@ -757,6 +758,11 @@ moduleFor(
     }
 
     ['@test renders with dot path and updates attributes'](assert) {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       this.registerComponent('my-nested-component', {
         ComponentClass: Component.extend({
           didReceiveAttrs() {
@@ -839,6 +845,14 @@ moduleFor(
     ['@test parameters in a contextual component are mutable when value is a param'](assert) {
       // This checks that a `(mut)` is added to parameters and attributes to
       // contextual components when it is a param.
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
 
       this.registerComponent('change-button', {
         ComponentClass: Component.extend().reopenClass({
@@ -889,6 +903,10 @@ moduleFor(
     }
 
     ['@test GH#13494 tagless blockless component with property binding'](assert) {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
       this.registerComponent('outer-component', {
         ComponentClass: Component.extend({
           message: 'hello',
@@ -1442,6 +1460,14 @@ class MutableParamTestGenerator {
   generate({ title, setup }) {
     return {
       [`@test parameters in a contextual component are mutable when value is a ${title}`](assert) {
+        expectDeprecation(
+          /Usage of the `\(action\)` helper is deprecated./,
+          DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+        );
+        expectDeprecation(
+          /Usage of the `\{\{action\}\}` modifier is deprecated./,
+          DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+        );
         this.registerComponent('change-button', {
           ComponentClass: Component.extend().reopenClass({
             positionalParams: ['val'],
diff --git a/packages/@ember/-internals/glimmer/tests/integration/components/curly-components-test.js b/packages/@ember/-internals/glimmer/tests/integration/components/curly-components-test.js
index d3646a33074..5eaf4c6cffd 100644
--- a/packages/@ember/-internals/glimmer/tests/integration/components/curly-components-test.js
+++ b/packages/@ember/-internals/glimmer/tests/integration/components/curly-components-test.js
@@ -20,6 +20,7 @@ import { A as emberA } from '@ember/array';
 
 import { Component, compile, htmlSafe } from '../../utils/helpers';
 import { backtrackingMessageFor } from '../../utils/debug-stack';
+import { DEPRECATIONS } from '../../../../deprecations';
 
 moduleFor(
   'Components test: curly components',
@@ -1428,6 +1429,11 @@ moduleFor(
     ) {
       let componentInstance = null;
 
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       this.registerComponent('non-block', {
         ComponentClass: Component.extend({
           counter: computed({
@@ -3149,6 +3155,11 @@ moduleFor(
     ['@test returning `true` from an action does not bubble if `target` is not specified (GH#14275)'](
       assert
     ) {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       this.registerComponent('display-toggle', {
         ComponentClass: Component.extend({
           actions: {
@@ -3174,7 +3185,12 @@ moduleFor(
     }
 
     ['@test returning `true` from an action bubbles to the `target` if specified'](assert) {
-      assert.expect(4);
+      assert.expect(5);
+
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
 
       this.registerComponent('display-toggle', {
         ComponentClass: Component.extend({
diff --git a/packages/@ember/-internals/glimmer/tests/integration/components/dynamic-components-test.js b/packages/@ember/-internals/glimmer/tests/integration/components/dynamic-components-test.js
index 7cf3d5aae22..c31dd97824c 100644
--- a/packages/@ember/-internals/glimmer/tests/integration/components/dynamic-components-test.js
+++ b/packages/@ember/-internals/glimmer/tests/integration/components/dynamic-components-test.js
@@ -5,6 +5,7 @@ import { set, computed } from '@ember/object';
 
 import { Component } from '../../utils/helpers';
 import { backtrackingMessageFor } from '../../utils/debug-stack';
+import { DEPRECATIONS } from '../../../../deprecations';
 
 moduleFor(
   'Components test: dynamic components',
@@ -449,6 +450,11 @@ moduleFor(
         }),
       });
 
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let actionTriggered = 0;
       this.registerComponent('outer-component', {
         template:
diff --git a/packages/@ember/-internals/glimmer/tests/integration/components/input-angle-test.js b/packages/@ember/-internals/glimmer/tests/integration/components/input-angle-test.js
index 88f20df47da..7f0e6de03ef 100644
--- a/packages/@ember/-internals/glimmer/tests/integration/components/input-angle-test.js
+++ b/packages/@ember/-internals/glimmer/tests/integration/components/input-angle-test.js
@@ -1,5 +1,6 @@
 import { moduleFor, RenderingTestCase, runDestroy, runTask } from 'internal-test-helpers';
 import { set } from '@ember/object';
+import { DEPRECATIONS } from '../../../../deprecations';
 
 class InputRenderingTest extends RenderingTestCase {
   $input() {
@@ -283,7 +284,11 @@ moduleFor(
     ['@test sends an action with `<Input @enter={{action "foo"}} />` when <enter> is pressed'](
       assert
     ) {
-      assert.expect(2);
+      assert.expect(3);
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
 
       this.render(`<Input @enter={{action 'foo'}} />`, {
         actions: {
@@ -300,7 +305,11 @@ moduleFor(
     }
 
     ['@test sends `insert-newline` when <enter> is pressed'](assert) {
-      assert.expect(2);
+      assert.expect(3);
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
 
       this.render(`<Input @insert-newline={{action 'foo'}} />`, {
         actions: {
@@ -319,7 +328,11 @@ moduleFor(
     ['@test sends an action with `<Input @escape-press={{action "foo"}} />` when <escape> is pressed'](
       assert
     ) {
-      assert.expect(2);
+      assert.expect(3);
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
 
       this.render(`<Input @escape-press={{action 'foo'}} />`, {
         actions: {
diff --git a/packages/@ember/-internals/glimmer/tests/integration/components/input-curly-test.js b/packages/@ember/-internals/glimmer/tests/integration/components/input-curly-test.js
index 1e8c4589cd9..0d9334250ab 100644
--- a/packages/@ember/-internals/glimmer/tests/integration/components/input-curly-test.js
+++ b/packages/@ember/-internals/glimmer/tests/integration/components/input-curly-test.js
@@ -1,6 +1,7 @@
 import { RenderingTestCase, moduleFor, runDestroy, runTask } from 'internal-test-helpers';
 
 import { set } from '@ember/object';
+import { DEPRECATIONS } from '../../../../deprecations';
 
 class InputRenderingTest extends RenderingTestCase {
   $input() {
@@ -152,7 +153,11 @@ moduleFor(
     ['@test sends an action with `{{input enter=(action "foo")}}` when <enter> is pressed'](
       assert
     ) {
-      assert.expect(2);
+      assert.expect(3);
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
 
       this.render(`{{input enter=(action 'foo')}}`, {
         actions: {
@@ -169,7 +174,11 @@ moduleFor(
     }
 
     ['@test sends `insert-newline` when <enter> is pressed'](assert) {
-      assert.expect(2);
+      assert.expect(3);
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
 
       this.render(`{{input insert-newline=(action 'foo')}}`, {
         actions: {
@@ -188,7 +197,11 @@ moduleFor(
     ['@test sends an action with `{{input escape-press=(action "foo")}}` when <escape> is pressed'](
       assert
     ) {
-      assert.expect(2);
+      assert.expect(3);
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
 
       this.render(`{{input escape-press=(action 'foo')}}`, {
         actions: {
diff --git a/packages/@ember/-internals/glimmer/tests/integration/components/link-to/routing-angle-test.js b/packages/@ember/-internals/glimmer/tests/integration/components/link-to/routing-angle-test.js
index 259cfe15b6d..eae9d9372b5 100644
--- a/packages/@ember/-internals/glimmer/tests/integration/components/link-to/routing-angle-test.js
+++ b/packages/@ember/-internals/glimmer/tests/integration/components/link-to/routing-angle-test.js
@@ -13,6 +13,7 @@ import { service } from '@ember/service';
 import Engine from '@ember/engine';
 import { DEBUG } from '@glimmer/env';
 import { compile } from '../../../utils/helpers';
+import { DEPRECATIONS } from '../../../../../deprecations';
 
 // IE includes the host name
 function normalizeUrl(url) {
@@ -1027,6 +1028,10 @@ moduleFor(
     }
 
     async ['@test it defaults to bubbling'](assert) {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
       this.addTemplate(
         'about',
         `
diff --git a/packages/@ember/-internals/glimmer/tests/integration/components/link-to/routing-curly-test.js b/packages/@ember/-internals/glimmer/tests/integration/components/link-to/routing-curly-test.js
index 86deedf092f..fb1e8441511 100644
--- a/packages/@ember/-internals/glimmer/tests/integration/components/link-to/routing-curly-test.js
+++ b/packages/@ember/-internals/glimmer/tests/integration/components/link-to/routing-curly-test.js
@@ -13,6 +13,7 @@ import { service } from '@ember/service';
 import Engine from '@ember/engine';
 import { DEBUG } from '@glimmer/env';
 import { compile } from '../../../utils/helpers';
+import { DEPRECATIONS } from '../../../../../deprecations';
 
 // IE includes the host name
 function normalizeUrl(url) {
@@ -1097,6 +1098,11 @@ moduleFor(
     }
 
     async ['@test it defaults to bubbling'](assert) {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       this.addTemplate(
         'about',
         `
diff --git a/packages/@ember/-internals/glimmer/tests/integration/components/tracked-test.js b/packages/@ember/-internals/glimmer/tests/integration/components/tracked-test.js
index 8a17d5d007b..45be3d38565 100644
--- a/packages/@ember/-internals/glimmer/tests/integration/components/tracked-test.js
+++ b/packages/@ember/-internals/glimmer/tests/integration/components/tracked-test.js
@@ -8,6 +8,7 @@ import { Promise } from 'rsvp';
 import { moduleFor, RenderingTestCase, strip, runTask } from 'internal-test-helpers';
 import GlimmerishComponent from '../../utils/glimmerish-component';
 import { Component } from '../../utils/helpers';
+import { DEPRECATIONS } from '../../../../deprecations';
 
 moduleFor(
   'Component Tracked Properties',
@@ -136,6 +137,11 @@ moduleFor(
     }
 
     '@test tracked properties that are uninitialized do not throw an error'() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let CountComponent = Component.extend({
         count: tracked(),
 
@@ -162,6 +168,11 @@ moduleFor(
     }
 
     '@test tracked properties rerender when updated'() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let CountComponent = Component.extend({
         count: tracked({ value: 0 }),
 
@@ -185,6 +196,11 @@ moduleFor(
     }
 
     '@test tracked properties rerender when updated outside of a runloop'(assert) {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let done = assert.async();
 
       let CountComponent = Component.extend({
@@ -216,6 +232,11 @@ moduleFor(
     }
 
     '@test nested tracked properties rerender when updated'() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let Counter = EmberObject.extend({
         count: tracked({ value: 0 }),
       });
@@ -243,6 +264,11 @@ moduleFor(
     }
 
     '@test array properties rerender when updated'() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let NumListComponent = Component.extend({
         numbers: tracked({ initializer: () => A([1, 2, 3]) }),
 
@@ -270,6 +296,11 @@ moduleFor(
     }
 
     '@test getters update when dependent properties are invalidated'() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let CountComponent = Component.extend({
         count: tracked({ value: 0 }),
 
@@ -299,6 +330,11 @@ moduleFor(
     }
 
     '@test getters update when dependent computeds are invalidated'() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let CountComponent = Component.extend({
         _count: 0,
 
@@ -340,6 +376,11 @@ moduleFor(
     }
 
     '@test nested getters update when dependent properties are invalidated'() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let Counter = EmberObject.extend({
         count: tracked({ value: 0 }),
 
@@ -373,6 +414,11 @@ moduleFor(
     }
 
     '@test tracked object passed down through components updates correctly'(assert) {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let Person = EmberObject.extend({
         first: tracked({ value: 'Rob' }),
         last: tracked({ value: 'Jackson' }),
@@ -423,6 +469,11 @@ moduleFor(
     }
 
     '@test yielded getters update correctly'() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let PersonComponent = Component.extend({
         first: tracked({ value: 'Rob' }),
         last: tracked({ value: 'Jackson' }),
@@ -462,6 +513,11 @@ moduleFor(
     }
 
     '@test yielded nested getters update correctly'() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let Person = EmberObject.extend({
         first: tracked({ value: 'Rob' }),
         last: tracked({ value: 'Jackson' }),
@@ -587,6 +643,11 @@ moduleFor(
     '@test downstream property changes do not invalidate upstream component getters/arguments'(
       assert
     ) {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let outerRenderCount = 0;
       let innerRenderCount = 0;
 
diff --git a/packages/@ember/-internals/glimmer/tests/integration/components/utils-test.js b/packages/@ember/-internals/glimmer/tests/integration/components/utils-test.js
index af536c1d7b7..a89d3d237a1 100644
--- a/packages/@ember/-internals/glimmer/tests/integration/components/utils-test.js
+++ b/packages/@ember/-internals/glimmer/tests/integration/components/utils-test.js
@@ -10,6 +10,7 @@ import {
 } from '@ember/-internals/views';
 
 import { Component } from '../../utils/helpers';
+import { DEPRECATIONS } from '../../../../deprecations';
 
 moduleFor(
   'View tree tests',
@@ -49,6 +50,11 @@ moduleFor(
         },
       });
 
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       this.add('controller:application', ToggleController);
 
       this.addTemplate(
diff --git a/packages/@ember/-internals/glimmer/tests/integration/event-dispatcher-test.js b/packages/@ember/-internals/glimmer/tests/integration/event-dispatcher-test.js
index c665be30561..e682e7b6563 100644
--- a/packages/@ember/-internals/glimmer/tests/integration/event-dispatcher-test.js
+++ b/packages/@ember/-internals/glimmer/tests/integration/event-dispatcher-test.js
@@ -2,6 +2,7 @@ import { moduleFor, RenderingTestCase, runTask } from 'internal-test-helpers';
 
 import { Component } from '../utils/helpers';
 import { _getCurrentRunLoop } from '@ember/runloop';
+import { DEPRECATIONS } from '../../../deprecations';
 
 let canDataTransfer = Boolean(document.createEvent('HTMLEvents').dataTransfer);
 
@@ -134,6 +135,11 @@ moduleFor(
     }
 
     ['@test case insensitive events'](assert) {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let receivedEvent;
 
       this.registerComponent('x-bar', {
@@ -153,6 +159,10 @@ moduleFor(
     }
 
     ['@test case sensitive events'](assert) {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
       let receivedEvent;
 
       this.registerComponent('x-bar', {
diff --git a/packages/@ember/-internals/glimmer/tests/integration/helpers/closure-action-test.js b/packages/@ember/-internals/glimmer/tests/integration/helpers/closure-action-test.js
index 491ec966116..626a0394ea5 100644
--- a/packages/@ember/-internals/glimmer/tests/integration/helpers/closure-action-test.js
+++ b/packages/@ember/-internals/glimmer/tests/integration/helpers/closure-action-test.js
@@ -4,11 +4,17 @@ import { _getCurrentRunLoop } from '@ember/runloop';
 import { set, computed } from '@ember/object';
 
 import { Component } from '../../utils/helpers';
+import { DEPRECATIONS } from '../../../../deprecations';
 
 moduleFor(
   'Helpers test: closure {{action}}',
   class extends RenderingTestCase {
     ['@test action should be called']() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let outerActionCalled = false;
       let component;
 
@@ -47,6 +53,11 @@ moduleFor(
     }
 
     ['@test an error is triggered when bound action function is undefined']() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       this.registerComponent('inner-component', {
         template: 'inner',
       });
@@ -60,6 +71,11 @@ moduleFor(
     }
 
     ['@test an error is triggered when bound action being passed in is a non-function']() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       this.registerComponent('inner-component', {
         template: 'inner',
       });
@@ -76,6 +92,15 @@ moduleFor(
     }
 
     ['@test [#12718] a nice error is shown when a bound action function is undefined and it is passed as @foo']() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       this.registerComponent('inner-component', {
         template:
           '<button id="inner-button" {{action (action @external-action)}}>Click me</button>',
@@ -91,6 +116,11 @@ moduleFor(
     }
 
     ['@test action value is returned']() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let expectedValue = 'terrible tom';
       let returnedValue;
       let innerComponent;
@@ -131,6 +161,11 @@ moduleFor(
     }
 
     ['@test action should be called on the correct scope']() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let innerComponent;
       let outerComponent;
       let actualComponent;
@@ -177,6 +212,11 @@ moduleFor(
     }
 
     ['@test arguments to action are passed, curry']() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let first = 'mitch';
       let second = 'martin';
       let third = 'matt';
@@ -226,6 +266,11 @@ moduleFor(
     }
 
     ['@test `this` can be passed as an argument']() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let value = {};
       let component;
       let innerComponent;
@@ -271,6 +316,11 @@ moduleFor(
     }
 
     ['@test arguments to action are bound']() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let value = 'lazy leah';
 
       let innerComponent;
@@ -328,6 +378,11 @@ moduleFor(
     }
 
     ['@test array arguments are passed correctly to action']() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let first = 'foo';
       let second = [3, 5];
       let third = [4, 9];
@@ -388,6 +443,11 @@ moduleFor(
     }
 
     ['@test mut values can be wrapped in actions, are settable']() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let newValue = 'trollin trek';
 
       let innerComponent;
@@ -431,6 +491,11 @@ moduleFor(
     }
 
     ['@test mut values can be wrapped in actions, are settable with a curry']() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let newValue = 'trollin trek';
 
       let innerComponent;
@@ -474,6 +539,11 @@ moduleFor(
     }
 
     ['@test action can create closures over actions']() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let first = 'raging robert';
       let second = 'mild machty';
       let returnValue = 'butch brian';
@@ -526,6 +596,11 @@ moduleFor(
     }
 
     ['@test provides a helpful error if an action is not present']() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let InnerComponent = Component.extend({});
 
       let OuterComponent = Component.extend({
@@ -554,6 +629,11 @@ moduleFor(
     }
 
     ['@test provides a helpful error if actions hash is not present']() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let InnerComponent = Component.extend({});
 
       let OuterComponent = Component.extend({});
@@ -574,6 +654,11 @@ moduleFor(
     }
 
     ['@test action can create closures over actions with target']() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let innerComponent;
       let actionCalled = false;
 
@@ -619,6 +704,11 @@ moduleFor(
     }
 
     ['@test value can be used with action over actions']() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let newValue = 'yelping yehuda';
 
       let innerComponent;
@@ -667,6 +757,11 @@ moduleFor(
     }
 
     ['@test action will read the value of a first property']() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let newValue = 'irate igor';
 
       let innerComponent;
@@ -710,6 +805,11 @@ moduleFor(
     }
 
     ['@test action will read the value of a curried first argument property']() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let newValue = 'kissing kris';
 
       let innerComponent;
@@ -754,6 +854,11 @@ moduleFor(
     }
 
     ['@test action closure does not get auto-mut wrapped'](assert) {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let first = 'raging robert';
       let second = 'mild machty';
       let returnValue = 'butch brian';
@@ -823,6 +928,11 @@ moduleFor(
     }
 
     ['@test action should be called within a run loop']() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let innerComponent;
       let capturedRunLoop;
 
@@ -864,6 +974,11 @@ moduleFor(
     }
 
     ['@test closure action with `(mut undefinedThing)` works properly [GH#13959]']() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let component;
 
       let ExampleComponent = Component.extend({
@@ -914,6 +1029,11 @@ moduleFor(
     ['@test closure actions does not cause component hooks to fire unnecessarily [GH#14305] [GH#14654]'](
       assert
     ) {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let clicked = 0;
       let didReceiveAttrsFired = 0;
 
diff --git a/packages/@ember/-internals/glimmer/tests/integration/helpers/element-action-test.js b/packages/@ember/-internals/glimmer/tests/integration/helpers/element-action-test.js
index d5b0728a0ed..72fa6f73f83 100644
--- a/packages/@ember/-internals/glimmer/tests/integration/helpers/element-action-test.js
+++ b/packages/@ember/-internals/glimmer/tests/integration/helpers/element-action-test.js
@@ -5,6 +5,7 @@ import { A as emberA } from '@ember/array';
 import { ActionManager } from '@ember/-internals/views';
 
 import { Component } from '../../utils/helpers';
+import { DEPRECATIONS } from '../../../../deprecations';
 
 function getActionAttributes(element) {
   let attributes = element.attributes;
@@ -31,6 +32,11 @@ moduleFor(
   'Helpers test: element action',
   class extends RenderingTestCase {
     ['@test it can call an action on its enclosing component']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let fooCallCount = 0;
 
       let ExampleComponent = Component.extend({
@@ -68,6 +74,11 @@ moduleFor(
     }
 
     ['@test it can call an action with parameters']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let fooArgs = [];
       let component;
 
@@ -115,6 +126,11 @@ moduleFor(
     }
 
     ['@test it should output a marker attribute with a guid']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       this.render('<button {{action "show"}}>me the money</button>');
 
       let button = this.$('button');
@@ -132,6 +148,11 @@ moduleFor(
     }
 
     ['@test it should allow alternative events to be handled']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let showCalled = false;
 
       let ExampleComponent = Component.extend({
@@ -157,6 +178,11 @@ moduleFor(
     }
 
     ['@test inside a yield, the target points at the original target']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let targetWatted = false;
       let innerWatted = false;
 
@@ -201,6 +227,11 @@ moduleFor(
     }
 
     ['@test it should allow a target to be specified']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let targetWatted = false;
 
       let TargetComponent = Component.extend({
@@ -237,6 +268,11 @@ moduleFor(
     }
 
     ['@test it should lazily evaluate the target']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let firstEdit = 0;
       let secondEdit = 0;
       let component;
@@ -287,6 +323,11 @@ moduleFor(
     }
 
     ['@test it should register an event handler']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let editHandlerWasCalled = false;
       let shortcutHandlerWasCalled = false;
 
@@ -327,6 +368,11 @@ moduleFor(
     }
 
     ['@test it handles whitelisted bound modifier keys']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let editHandlerWasCalled = false;
       let shortcutHandlerWasCalled = false;
 
@@ -369,6 +415,11 @@ moduleFor(
     }
 
     ['@test it handles whitelisted bound modifier keys with current value']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let editHandlerWasCalled = false;
       let component;
 
@@ -412,6 +463,11 @@ moduleFor(
     }
 
     ['@test should be able to use action more than once for the same event within a view']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let editHandlerWasCalled = false;
       let deleteHandlerWasCalled = false;
       let originalHandlerWasCalled = false;
@@ -481,6 +537,11 @@ moduleFor(
     }
 
     ['@test the event should not bubble if `bubbles=false` is passed']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let editHandlerWasCalled = false;
       let deleteHandlerWasCalled = false;
       let originalHandlerWasCalled = false;
@@ -542,6 +603,11 @@ moduleFor(
     }
 
     ['@test the event should not bubble if `bubbles=false` is passed bound']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let editHandlerWasCalled = false;
       let deleteHandlerWasCalled = false;
       let originalHandlerWasCalled = false;
@@ -604,6 +670,11 @@ moduleFor(
     }
 
     ['@test the bubbling depends on the bound parameter']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let editHandlerWasCalled = false;
       let originalHandlerWasCalled = false;
       let component;
@@ -653,6 +724,11 @@ moduleFor(
     }
 
     ['@test multiple actions with bubbles=false for same event are called but prevent bubbling']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let clickAction1WasCalled = false;
       let clickAction2WasCalled = false;
       let eventHandlerWasCalled = false;
@@ -692,6 +768,11 @@ moduleFor(
     }
 
     ['@test it should work properly in an #each block']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let editHandlerWasCalled = false;
 
       let ExampleComponent = Component.extend({
@@ -719,6 +800,11 @@ moduleFor(
     }
 
     ['@test it should work properly in a {{#let foo as |bar|}} block']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let editHandlerWasCalled = false;
 
       let ExampleComponent = Component.extend({
@@ -746,6 +832,11 @@ moduleFor(
     }
 
     ['@test it should unregister event handlers when an element action is removed'](assert) {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let ExampleComponent = Component.extend({
         actions: {
           edit() {},
@@ -791,6 +882,11 @@ moduleFor(
     }
 
     ['@test it should capture events from child elements and allow them to trigger the action']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let editHandlerWasCalled = false;
 
       let ExampleComponent = Component.extend({
@@ -819,6 +915,11 @@ moduleFor(
     }
 
     ['@test it should allow bubbling of events from action helper to original parent event']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let editHandlerWasCalled = false;
       let originalHandlerWasCalled = false;
 
@@ -851,6 +952,11 @@ moduleFor(
     }
 
     ['@test it should not bubble an event from action helper to original parent event if `bubbles=false` is passed']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let editHandlerWasCalled = false;
       let originalHandlerWasCalled = false;
 
@@ -881,6 +987,11 @@ moduleFor(
     }
 
     ['@test it should allow "send" as the action name (#594)']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let sendHandlerWasCalled = false;
 
       let ExampleComponent = Component.extend({
@@ -906,6 +1017,11 @@ moduleFor(
     }
 
     ['@test it should send the view, event, and current context to the action']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let passedTarget;
       let passedContext;
       let targetThis;
@@ -957,6 +1073,11 @@ moduleFor(
     }
 
     ['@test it should only trigger actions for the event they were registered on']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let editHandlerWasCalled = false;
 
       let ExampleComponent = Component.extend({
@@ -990,6 +1111,11 @@ moduleFor(
     }
 
     ['@test it should allow multiple contexts to be specified']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let passedContexts;
       let models = [EmberObject.create(), EmberObject.create()];
 
@@ -1022,6 +1148,11 @@ moduleFor(
     }
 
     ['@test it should allow multiple contexts to be specified mixed with string args']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let passedContexts;
       let model = EmberObject.create();
 
@@ -1053,6 +1184,11 @@ moduleFor(
     }
 
     ['@test it should not trigger action with special clicks']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let showCalled = false;
       let component;
 
@@ -1104,6 +1240,11 @@ moduleFor(
     }
 
     ['@test it can trigger actions for keyboard events']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let showCalled = false;
 
       let ExampleComponent = Component.extend({
@@ -1129,6 +1270,11 @@ moduleFor(
     }
 
     ['@test a quoteless parameter should allow dynamic lookup of the actionName']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let lastAction;
       let actionOrder = [];
       let component;
@@ -1188,6 +1334,11 @@ moduleFor(
     }
 
     ['@test a quoteless string parameter should resolve actionName, including path']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let lastAction;
       let actionOrder = [];
       let component;
@@ -1248,6 +1399,11 @@ moduleFor(
     }
 
     ['@test a quoteless function parameter should be called, including arguments']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let submitCalled = false;
       let incomingArg;
 
@@ -1276,6 +1432,11 @@ moduleFor(
     }
 
     ['@test a quoteless parameter that does not resolve to a value asserts']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let ExampleComponent = Component.extend({
         actions: {
           ohNoeNotValid() {},
@@ -1293,6 +1454,11 @@ moduleFor(
     }
 
     ['@test allows multiple actions on a single element']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let clickActionWasCalled = false;
       let doubleClickActionWasCalled = false;
 
@@ -1332,6 +1498,11 @@ moduleFor(
     }
 
     ['@test allows multiple actions for same event on a single element']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let clickAction1WasCalled = false;
       let clickAction2WasCalled = false;
 
@@ -1366,6 +1537,11 @@ moduleFor(
     }
 
     ['@test it should respect preventDefault option if provided']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let ExampleComponent = Component.extend({
         actions: {
           show() {},
@@ -1389,6 +1565,11 @@ moduleFor(
     }
 
     ['@test it should respect preventDefault option if provided bound']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let component;
 
       let ExampleComponent = Component.extend({
@@ -1426,6 +1607,11 @@ moduleFor(
     }
 
     ['@test it should target the proper component when `action` is in yielded block [GH #12409]']() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let outerActionCalled = false;
       let innerClickCalled = false;
 
@@ -1479,6 +1665,11 @@ moduleFor(
     }
 
     ['@test element action with (mut undefinedThing) works properly']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let component;
 
       let ExampleComponent = Component.extend({
@@ -1527,6 +1718,11 @@ moduleFor(
     }
 
     ['@test it supports non-registered actions [GH#14888]']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       this.render(
         `
       {{#if this.show}}
@@ -1547,6 +1743,11 @@ moduleFor(
     }
 
     ["@test action handler that shifts element attributes doesn't trigger multiple invocations"]() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let actionCount = 0;
       let ExampleComponent = Component.extend({
         selected: false,
diff --git a/packages/@ember/-internals/glimmer/tests/integration/helpers/fn-test.js b/packages/@ember/-internals/glimmer/tests/integration/helpers/fn-test.js
index a2aa0b74eda..ead9cdb2dca 100644
--- a/packages/@ember/-internals/glimmer/tests/integration/helpers/fn-test.js
+++ b/packages/@ember/-internals/glimmer/tests/integration/helpers/fn-test.js
@@ -2,6 +2,7 @@ import { set } from '@ember/object';
 import { DEBUG } from '@glimmer/env';
 import { RenderingTestCase, moduleFor, runTask } from 'internal-test-helpers';
 import { Component } from '../../utils/helpers';
+import { DEPRECATIONS } from '../../../../deprecations';
 
 moduleFor(
   'Helpers test: {{fn}}',
@@ -135,6 +136,10 @@ moduleFor(
     }
 
     '@test can use `this` if bound prior to passing to fn'(assert) {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
       this.render(`{{stash stashedFn=(fn (action this.myFunc) this.arg1)}}`, {
         myFunc(arg1) {
           return `arg1: ${arg1}, arg2: ${this.arg2}`;
diff --git a/packages/@ember/-internals/glimmer/tests/integration/helpers/readonly-test.js b/packages/@ember/-internals/glimmer/tests/integration/helpers/readonly-test.js
index aa6415d37cc..81937c7d8dd 100644
--- a/packages/@ember/-internals/glimmer/tests/integration/helpers/readonly-test.js
+++ b/packages/@ember/-internals/glimmer/tests/integration/helpers/readonly-test.js
@@ -3,6 +3,7 @@ import { RenderingTestCase, moduleFor, runTask } from 'internal-test-helpers';
 import { set, get } from '@ember/object';
 
 import { Component } from '../../utils/helpers';
+import { DEPRECATIONS } from '../../../../deprecations';
 
 moduleFor(
   'Helpers test: {{readonly}}',
@@ -37,7 +38,12 @@ moduleFor(
     }
 
     '@test passing an action to {{readonly}} avoids mutable cell wrapping'(assert) {
-      assert.expect(4);
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
+      assert.expect(5);
       let outer, inner;
 
       this.registerComponent('x-inner', {
diff --git a/packages/@ember/-internals/glimmer/tests/integration/helpers/tracked-test.js b/packages/@ember/-internals/glimmer/tests/integration/helpers/tracked-test.js
index 8fe282cbbbc..e196e1e4163 100644
--- a/packages/@ember/-internals/glimmer/tests/integration/helpers/tracked-test.js
+++ b/packages/@ember/-internals/glimmer/tests/integration/helpers/tracked-test.js
@@ -10,11 +10,16 @@ import Service, { service } from '@ember/service';
 import { moduleFor, RenderingTestCase, strip, runTask } from 'internal-test-helpers';
 
 import { Component } from '../../utils/helpers';
+import { DEPRECATIONS } from '../../../../deprecations';
 
 moduleFor(
   'Helper Tracked Properties',
   class extends RenderingTestCase {
     '@test tracked properties rerender when updated'(assert) {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
       let computeCount = 0;
 
       let PersonComponent = Component.extend({
@@ -92,6 +97,10 @@ moduleFor(
     }
 
     '@test getters update when dependent properties are invalidated'(assert) {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
       let computeCount = 0;
 
       let PersonComponent = Component.extend({
@@ -144,6 +153,10 @@ moduleFor(
     }
 
     '@test array properties rerender when updated'() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
       let NumListComponent = Component.extend({
         numbers: tracked({ initializer: () => A([1, 2, 3]) }),
 
@@ -175,6 +188,10 @@ moduleFor(
     }
 
     '@test custom ember array properties rerender when updated'() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
       let CustomArray = EmberObject.extend(MutableArray, {
         init() {
           this._super(...arguments);
diff --git a/packages/@ember/-internals/glimmer/tests/integration/input-test.js b/packages/@ember/-internals/glimmer/tests/integration/input-test.js
index 731a01763b8..87aa1668219 100644
--- a/packages/@ember/-internals/glimmer/tests/integration/input-test.js
+++ b/packages/@ember/-internals/glimmer/tests/integration/input-test.js
@@ -1,4 +1,5 @@
 import { RenderingTestCase, moduleFor, runTask } from 'internal-test-helpers';
+import { DEPRECATIONS } from '../../../deprecations';
 
 import { set } from '@ember/object';
 
@@ -202,6 +203,10 @@ moduleFor(
     }
 
     ['@test GH18211 input checked attribute, without a value, works with the action helper']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
       this.render(`<input type="checkbox" checked {{action "someAction"}}>`, {
         actions: { someAction() {} },
       });
@@ -209,6 +214,10 @@ moduleFor(
     }
 
     ['@test GH18211 input checked attribute, with a value, works with the action helper']() {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
       this.render(`<input type="checkbox" checked={{true}} {{action "someAction"}}>`, {
         actions: { someAction() {} },
       });
@@ -216,6 +225,10 @@ moduleFor(
     }
 
     ['@test GH18211 input checked attribute, without a value, works with attributes with values']() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
       this.render(`<input type="checkbox" checked click={{action "someAction"}}>`, {
         actions: { someAction() {} },
       });
@@ -223,6 +236,10 @@ moduleFor(
     }
 
     ['@test GH18211 input checked attribute, without a value, works with event attributes']() {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
       this.render(`<input type="checkbox" checked onclick={{action "someAction"}}>`, {
         actions: { someAction() {} },
       });
diff --git a/packages/@ember/application/tests/visit_test.js b/packages/@ember/application/tests/visit_test.js
index 7b0887c28a7..f4ad9ed133c 100644
--- a/packages/@ember/application/tests/visit_test.js
+++ b/packages/@ember/application/tests/visit_test.js
@@ -15,6 +15,7 @@ import Route from '@ember/routing/route';
 import { Component, helper, isSerializationFirstNode } from '@ember/-internals/glimmer';
 import { compile } from 'ember-template-compiler';
 import { ENV } from '@ember/-internals/environment';
+import { DEPRECATIONS } from '@ember/-internals/deprecations';
 
 function expectAsyncError() {
   RSVP.off('error');
@@ -625,6 +626,10 @@ moduleFor(
     }
 
     [`@test Ember Islands-style setup`](assert) {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
       let xFooInitCalled = false;
       let xFooDidInsertElementCalled = false;
 
diff --git a/packages/@ember/canary-features/index.ts b/packages/@ember/canary-features/index.ts
index 89132270986..469bbaa7ffc 100644
--- a/packages/@ember/canary-features/index.ts
+++ b/packages/@ember/canary-features/index.ts
@@ -62,5 +62,3 @@ export function isEnabled(feature: string): boolean {
 
 //   return value;
 // }
-
-// export const FLAG_NAME = featureValue(FEATURES.FLAG_NAME);
diff --git a/packages/@ember/object/tests/action_test.js b/packages/@ember/object/tests/action_test.js
index 8acc0dca4de..59be6c64251 100644
--- a/packages/@ember/object/tests/action_test.js
+++ b/packages/@ember/object/tests/action_test.js
@@ -1,11 +1,17 @@
 import { Component } from '@ember/-internals/glimmer';
 import EmberObject, { action } from '@ember/object';
 import { moduleFor, RenderingTestCase, strip } from 'internal-test-helpers';
+import { DEPRECATIONS } from '@ember/-internals/deprecations';
 
 moduleFor(
   '@action decorator',
   class extends RenderingTestCase {
     '@test action decorator works with ES6 class'(assert) {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       class FooComponent extends Component {
         @action
         foo() {
@@ -49,7 +55,11 @@ moduleFor(
     }
 
     '@test actions are properly merged through traditional and ES6 prototype hierarchy'(assert) {
-      assert.expect(4);
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+      assert.expect(5);
 
       let FooComponent = Component.extend({
         actions: {
@@ -97,6 +107,11 @@ moduleFor(
     }
 
     '@test action decorator super works with native class methods'(assert) {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       class FooComponent extends Component {
         foo() {
           assert.ok(true, 'called!');
@@ -121,6 +136,11 @@ moduleFor(
     }
 
     '@test action decorator super works with traditional class methods'(assert) {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let FooComponent = Component.extend({
         foo() {
           assert.ok(true, 'called!');
@@ -239,6 +259,11 @@ moduleFor(
     }
 
     '@test action decorator can be used as a classic decorator with strings'(assert) {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+
       let FooComponent = Component.extend({
         foo: action(function () {
           assert.ok(true, 'called!');
diff --git a/packages/ember/tests/component_context_test.js b/packages/ember/tests/component_context_test.js
index fa88436a09e..2b8dc62f774 100644
--- a/packages/ember/tests/component_context_test.js
+++ b/packages/ember/tests/component_context_test.js
@@ -1,6 +1,7 @@
 import Controller from '@ember/controller';
 import { Component } from '@ember/-internals/glimmer';
 import { moduleFor, ApplicationTestCase, getTextOf } from 'internal-test-helpers';
+import { DEPRECATIONS } from '@ember/-internals/deprecations';
 
 moduleFor(
   'Application Lifecycle - Component Context',
@@ -186,6 +187,10 @@ moduleFor(
     ['@test Components trigger actions in the parents context when called from within a block'](
       assert
     ) {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
       this.addTemplate(
         'application',
         `
@@ -219,6 +224,10 @@ moduleFor(
     ['@test Components trigger actions in the components context when called from within its template'](
       assert
     ) {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
       this.addTemplate(
         'application',
         `
diff --git a/packages/ember/tests/controller_test.js b/packages/ember/tests/controller_test.js
index 26c8a020a94..ecb19bf319c 100644
--- a/packages/ember/tests/controller_test.js
+++ b/packages/ember/tests/controller_test.js
@@ -1,6 +1,7 @@
 import Controller from '@ember/controller';
 import { moduleFor, ApplicationTestCase, runTask } from 'internal-test-helpers';
 import { Component } from '@ember/-internals/glimmer';
+import { DEPRECATIONS } from '@ember/-internals/deprecations';
 
 /*
  In Ember 1.x, controllers subtly affect things like template scope
@@ -14,6 +15,10 @@ moduleFor(
   'Template scoping examples',
   class extends ApplicationTestCase {
     ['@test Actions inside an outlet go to the associated controller'](assert) {
+      expectDeprecation(
+        /Usage of the `\(action\)` helper is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
       this.add(
         'controller:index',
         Controller.extend({
diff --git a/packages/ember/tests/integration/multiple-app-test.js b/packages/ember/tests/integration/multiple-app-test.js
index b151999936a..9ffad291a16 100644
--- a/packages/ember/tests/integration/multiple-app-test.js
+++ b/packages/ember/tests/integration/multiple-app-test.js
@@ -3,6 +3,7 @@ import Application from '@ember/application';
 import { Component } from '@ember/-internals/glimmer';
 import { getOwner } from '@ember/-internals/owner';
 import { resolve } from 'rsvp';
+import { DEPRECATIONS } from '@ember/-internals/deprecations';
 
 moduleFor(
   'View Integration',
@@ -82,6 +83,10 @@ moduleFor(
     }
 
     [`@test booting multiple applications can properly handle events`](assert) {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
       let actions = [];
       this.addFactoriesToResolver(actions, this.resolver);
       this.addFactoriesToResolver(actions, this.secondResolver);
diff --git a/packages/ember/tests/routing/decoupled_basic_test.js b/packages/ember/tests/routing/decoupled_basic_test.js
index 9e1888876d4..1a716f21339 100644
--- a/packages/ember/tests/routing/decoupled_basic_test.js
+++ b/packages/ember/tests/routing/decoupled_basic_test.js
@@ -6,6 +6,7 @@ import Route from '@ember/routing/route';
 import NoneLocation from '@ember/routing/none-location';
 import HistoryLocation from '@ember/routing/history-location';
 import Controller from '@ember/controller';
+import { DEPRECATIONS } from '@ember/-internals/deprecations';
 import EmberObject, { set } from '@ember/object';
 import {
   moduleFor,
@@ -296,6 +297,10 @@ moduleFor(
     async ['@test Events are triggered on the controller if a matching action name is implemented'](
       assert
     ) {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
       let done = assert.async();
 
       this.router.map(function () {
@@ -342,6 +347,10 @@ moduleFor(
     async ['@test Events are triggered on the current state when defined in `actions` object'](
       assert
     ) {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
       let done = assert.async();
 
       this.router.map(function () {
@@ -378,6 +387,10 @@ moduleFor(
     async ['@test Events defined in `actions` object are triggered on the current state when routes are nested'](
       assert
     ) {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
       let done = assert.async();
 
       this.router.map(function () {
@@ -419,7 +432,11 @@ moduleFor(
     }
 
     ['@test Events can be handled by inherited event handlers'](assert) {
-      assert.expect(4);
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+      assert.expect(5);
 
       let SuperRoute = Route.extend({
         actions: {
@@ -471,6 +488,10 @@ moduleFor(
     async ['@test Actions are not triggered on the controller if a matching action name is implemented as a method'](
       assert
     ) {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
       let done = assert.async();
 
       this.router.map(function () {
@@ -515,6 +536,10 @@ moduleFor(
     }
 
     async ['@test actions can be triggered with multiple arguments'](assert) {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
       let done = assert.async();
       this.router.map(function () {
         this.route('root', { path: '/' }, function () {
@@ -1213,7 +1238,11 @@ moduleFor(
     }
 
     ['@test Actions can be handled by inherited action handlers'](assert) {
-      assert.expect(4);
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
+      assert.expect(5);
 
       let SuperRoute = Route.extend({
         actions: {
diff --git a/packages/ember/tests/routing/query_params_test.js b/packages/ember/tests/routing/query_params_test.js
index 4f820f86996..43c12e3799a 100644
--- a/packages/ember/tests/routing/query_params_test.js
+++ b/packages/ember/tests/routing/query_params_test.js
@@ -8,6 +8,7 @@ import { peekMeta } from '@ember/-internals/meta';
 import { tracked } from '@ember/-internals/metal';
 import Route from '@ember/routing/route';
 import { PARAMS_SYMBOL } from 'router_js';
+import { DEPRECATIONS } from '@ember/-internals/deprecations';
 import { service } from '@ember/service';
 
 import { QueryParamTestCase, moduleFor, getTextOf, runLoopSettled } from 'internal-test-helpers';
@@ -743,6 +744,10 @@ moduleFor(
     async ['@test queryParams are updated when a controller property is set and the route is refreshed. Issue #13263  '](
       assert
     ) {
+      expectDeprecation(
+        /Usage of the `\{\{action\}\}` modifier is deprecated./,
+        DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isEnabled
+      );
       this.addTemplate(
         'application',
         '<button id="test-button" {{action \'increment\'}}>Increment</button><span id="test-value">{{this.foo}}</span>{{outlet}}'