diff --git a/client/my-sites/themes/activation-modal.jsx b/client/my-sites/themes/activation-modal.jsx
index e7c57d75d99c..7be1afb10847 100644
--- a/client/my-sites/themes/activation-modal.jsx
+++ b/client/my-sites/themes/activation-modal.jsx
@@ -1,25 +1,30 @@
 import { recordTracksEvent } from '@automattic/calypso-analytics';
-import { Dialog, Gridicon, Button, ScreenReaderText } from '@automattic/components';
+import { getPlan } from '@automattic/calypso-products';
+import { Button, Dialog, Gridicon, ScreenReaderText } from '@automattic/components';
 import { Onboard } from '@automattic/data-stores';
 import { localizeUrl } from '@automattic/i18n-utils';
+import { CheckboxControl } from '@wordpress/components';
 import { translate } from 'i18n-calypso';
 import PropTypes from 'prop-types';
 import { Component } from 'react';
 import { connect } from 'react-redux';
+import { THEME_TIERS } from 'calypso/components/theme-tier/constants';
 import TrackComponentView from 'calypso/lib/analytics/track-component-view';
 import { getSiteDomain } from 'calypso/state/sites/selectors';
 import {
 	acceptActivationModal,
-	dismissActivationModal,
 	activate as activateTheme,
+	dismissActivationModal,
 } from 'calypso/state/themes/actions';
 import {
+	getActiveTheme,
 	getCanonicalTheme,
+	getThemeIdToActivate,
+	getThemeTierForTheme,
 	isActivatingTheme,
 	isThemeActive,
+	isThemeAllowedOnSite,
 	shouldShowActivationModal,
-	getThemeIdToActivate,
-	getActiveTheme,
 } from 'calypso/state/themes/selectors';
 import { getSelectedSiteId } from 'calypso/state/ui/selectors';
 
@@ -45,21 +50,43 @@ export class ActivationModal extends Component {
 		newThemeId: PropTypes.string,
 	};
 
+	constructor( props ) {
+		super( props );
+		const { isCurrentThemeAllowedOnSite } = props;
+
+		this.state = {
+			checkboxChecked: isCurrentThemeAllowedOnSite,
+		};
+	}
+
+	onCheckboxChange = ( isChecked ) => {
+		this.setState( { checkboxChecked: isChecked } );
+	};
+
 	closeModalHandler =
 		( action = 'dismiss' ) =>
 		() => {
-			const { newThemeId, siteId, source } = this.props;
+			const { newThemeId, activeTheme, siteId, source, isCurrentThemeAllowedOnSite } = this.props;
 			if ( 'activeTheme' === action ) {
 				this.props.acceptActivationModal( newThemeId );
+				const eventName = ! isCurrentThemeAllowedOnSite
+					? 'calypso_theme_switch_plan_warning_accepted'
+					: 'calypso_theme_autoloading_homepage_modal_activate_click';
 
-				recordTracksEvent( 'calypso_theme_autoloading_homepage_modal_activate_click', {
+				recordTracksEvent( eventName, {
 					theme: newThemeId,
+					activeTheme: activeTheme.id,
 				} );
 				return this.props.activateTheme( newThemeId, siteId, { source } );
 			} else if ( 'dismiss' === action ) {
-				recordTracksEvent( 'calypso_theme_autoloading_homepage_modal_dismiss', {
+				const eventName = ! isCurrentThemeAllowedOnSite
+					? 'calypso_theme_switch_plan_warning_declined'
+					: 'calypso_theme_autoloading_homepage_modal_dismiss';
+
+				recordTracksEvent( eventName, {
 					action: 'escape',
 					theme: newThemeId,
+					activeTheme: activeTheme.id,
 				} );
 				return this.props.dismissActivationModal();
 			}
@@ -67,6 +94,8 @@ export class ActivationModal extends Component {
 
 	render() {
 		const {
+			isCurrentThemeAllowedOnSite,
+			activeThemeRequiredPlan,
 			newTheme,
 			activeTheme,
 			isActivating,
@@ -89,6 +118,10 @@ export class ActivationModal extends Component {
 			return null;
 		}
 
+		const eventName = ! isCurrentThemeAllowedOnSite
+			? 'calypso_theme_switch_plan_warning_modal_view'
+			: 'calypso_theme_autoloading_homepage_modal_view';
+
 		const isAIAssembler = siteIntent === SiteIntent.AIAssembler && activeTheme.id === 'assembler';
 		const translationArgs = {
 			args: {
@@ -127,8 +160,8 @@ export class ActivationModal extends Component {
 				onClose={ this.closeModalHandler( 'dismiss' ) }
 			>
 				<TrackComponentView
-					eventName="calypso_theme_autoloading_homepage_modal_view"
-					eventProperties={ { theme: newTheme.id } }
+					eventName={ eventName }
+					eventProperties={ { theme: newTheme.id, activeTheme: activeTheme.id } }
 				/>
 				<Button
 					className="themes__activation-modal-close-icon"
@@ -145,8 +178,34 @@ export class ActivationModal extends Component {
 						} ) }
 					</h1>
 					<p className="activation-modal__description">{ message }</p>
+					{ ! isCurrentThemeAllowedOnSite && (
+						<CheckboxControl
+							className="activation-modal__lower-tier-warning"
+							checked={ this.state.checkboxChecked }
+							onChange={ this.onCheckboxChange }
+							label={ translate(
+								'I understand I will not be able to switch back to %(themeName)s without upgrading my plan.',
+								{
+									args: { themeName: activeTheme.name },
+								}
+							) }
+							help={
+								activeThemeRequiredPlan &&
+								translate(
+									"%(themeName)s is no longer included in your plan, so you won't be able to activate it again unless you upgrade to the %(plan)s plan.",
+									{
+										args: { plan: activeThemeRequiredPlan.getTitle(), themeName: activeTheme.name },
+									}
+								)
+							}
+						/>
+					) }
 					<div className="activation-modal__actions">
-						<Button primary onClick={ this.closeModalHandler( 'activeTheme' ) }>
+						<Button
+							primary
+							disabled={ ! this.state.checkboxChecked }
+							onClick={ this.closeModalHandler( 'activeTheme' ) }
+						>
 							{ translate( 'Activate %(themeName)s', {
 								args: { themeName: newTheme.name },
 							} ) }
@@ -163,6 +222,11 @@ export default connect(
 		const siteId = getSelectedSiteId( state );
 		const newThemeId = getThemeIdToActivate( state );
 		const activeThemeId = getActiveTheme( state, siteId );
+		const isCurrentThemeAllowedOnSite = isThemeAllowedOnSite( state, siteId, activeThemeId );
+		const activeThemeTier = getThemeTierForTheme( state, activeThemeId );
+		const activeThemeMinimumUpsellPlan = THEME_TIERS[ activeThemeTier?.slug ]?.minimumUpsellPlan;
+		const activeThemeRequiredPlan =
+			activeThemeMinimumUpsellPlan && getPlan( activeThemeMinimumUpsellPlan );
 
 		return {
 			siteId,
@@ -173,6 +237,8 @@ export default connect(
 			isActivating: !! isActivatingTheme( state, siteId ),
 			isCurrentTheme: isThemeActive( state, newThemeId, siteId ),
 			isVisible: shouldShowActivationModal( state, newThemeId ),
+			isCurrentThemeAllowedOnSite,
+			activeThemeRequiredPlan,
 		};
 	},
 	{
diff --git a/client/my-sites/themes/activation-modal.scss b/client/my-sites/themes/activation-modal.scss
index c064a03b0173..312e21b23975 100644
--- a/client/my-sites/themes/activation-modal.scss
+++ b/client/my-sites/themes/activation-modal.scss
@@ -13,6 +13,10 @@
 	}
 }
 
+.activation-modal__lower-tier-warning {
+	margin-bottom: 36px;
+}
+
 .themes__activation-modal-close-icon {
 	position: absolute;
 	top: 4px;
diff --git a/client/state/themes/hooks/use-is-theme-allowed-on-site.ts b/client/state/themes/hooks/use-is-theme-allowed-on-site.ts
index 1b3cc7e9d58e..eba970b568e7 100644
--- a/client/state/themes/hooks/use-is-theme-allowed-on-site.ts
+++ b/client/state/themes/hooks/use-is-theme-allowed-on-site.ts
@@ -1,17 +1,8 @@
 import { useSelector } from 'calypso/state';
-import siteHasFeature from 'calypso/state/selectors/site-has-feature';
-import { getThemeTierForTheme } from 'calypso/state/themes/selectors';
+import { isThemeAllowedOnSite } from 'calypso/state/themes/selectors/is-theme-allowed-on-site';
 
 export function useIsThemeAllowedOnSite( siteId: number | null, themeId: string ) {
-	return useSelector( ( state ) => {
-		const themeTier = getThemeTierForTheme( state, themeId );
-		const features = themeTier?.featureList ?? [ themeTier?.feature ];
-
-		return features.some(
-			( feature: string | null | undefined ) =>
-				! feature || siteHasFeature( state, siteId, feature )
-		);
-	} );
+	return useSelector( ( state ) => isThemeAllowedOnSite( state, siteId, themeId ) );
 
 	/* @SEE https://github.com/Automattic/dotcom-forge/issues/8028
 	const retainedBenefits = useTierRetainedBenefitsQuery( siteId, themeId );
diff --git a/client/state/themes/selectors/index.js b/client/state/themes/selectors/index.js
index ab5623e4f6fc..f30cad5937f8 100644
--- a/client/state/themes/selectors/index.js
+++ b/client/state/themes/selectors/index.js
@@ -65,6 +65,7 @@ export { isSiteEligibleForBundledSoftware } from 'calypso/state/themes/selectors
 export { isSiteEligibleForManagedExternalThemes } from 'calypso/state/themes/selectors/is-site-eligible-for-managed-external-themes';
 export { isThemeActivationSyncStarted } from 'calypso/state/themes/selectors/is-theme-activation-sync-started';
 export { isThemeActive } from 'calypso/state/themes/selectors/is-theme-active';
+export { isThemeAllowedOnSite } from 'calypso/state/themes/selectors/is-theme-allowed-on-site';
 export { isThemeGutenbergFirst } from 'calypso/state/themes/selectors/is-theme-gutenberg-first';
 export { isThemePremium } from 'calypso/state/themes/selectors/is-theme-premium';
 export { isThemePurchased } from 'calypso/state/themes/selectors/is-theme-purchased';
diff --git a/client/state/themes/selectors/is-theme-allowed-on-site.ts b/client/state/themes/selectors/is-theme-allowed-on-site.ts
new file mode 100644
index 000000000000..eb5ef6949c1f
--- /dev/null
+++ b/client/state/themes/selectors/is-theme-allowed-on-site.ts
@@ -0,0 +1,12 @@
+import siteHasFeature from 'calypso/state/selectors/site-has-feature';
+import { getThemeTierForTheme } from 'calypso/state/themes/selectors';
+import { IAppState } from 'calypso/state/types';
+
+export function isThemeAllowedOnSite( state: IAppState, siteId: number | null, themeId: string ) {
+	const themeTier = getThemeTierForTheme( state, themeId );
+	const features = themeTier?.featureList ?? [ themeTier?.feature ];
+
+	return features.some(
+		( feature: string | null | undefined ) => ! feature || siteHasFeature( state, siteId, feature )
+	);
+}