diff --git a/packages/react-native-codegen/src/generators/modules/GenerateModuleJavaSpec.js b/packages/react-native-codegen/src/generators/modules/GenerateModuleJavaSpec.js
index 8ef4278dbc9954..bb1ee1311ae2af 100644
--- a/packages/react-native-codegen/src/generators/modules/GenerateModuleJavaSpec.js
+++ b/packages/react-native-codegen/src/generators/modules/GenerateModuleJavaSpec.js
@@ -148,6 +148,20 @@ function translateFunctionParamToJavaType(
         default:
           throw new Error(createErrorMessage(realTypeAnnotation.type));
       }
+    case 'UnionTypeAnnotation':
+      switch (typeAnnotation.memberType) {
+        case 'NumberTypeAnnotation':
+          return wrapNullable('double', 'Double');
+        case 'ObjectTypeAnnotation':
+          imports.add('com.facebook.react.bridge.ReadableMap');
+          return wrapNullable('ReadableMap');
+        case 'StringTypeAnnotation':
+          return wrapNullable('String');
+        default:
+          throw new Error(
+            `Unsupported union member returning value, found: ${realTypeAnnotation.memberType}"`,
+          );
+      }
     case 'ObjectTypeAnnotation':
       imports.add('com.facebook.react.bridge.ReadableMap');
       return wrapNullable('ReadableMap');
@@ -162,10 +176,7 @@ function translateFunctionParamToJavaType(
       imports.add('com.facebook.react.bridge.Callback');
       return wrapNullable('Callback');
     default:
-      (realTypeAnnotation.type:
-        | 'EnumDeclaration'
-        | 'MixedTypeAnnotation'
-        | 'UnionTypeAnnotation');
+      (realTypeAnnotation.type: 'EnumDeclaration' | 'MixedTypeAnnotation');
       throw new Error(createErrorMessage(realTypeAnnotation.type));
   }
 }
@@ -229,6 +240,20 @@ function translateFunctionReturnTypeToJavaType(
         default:
           throw new Error(createErrorMessage(realTypeAnnotation.type));
       }
+    case 'UnionTypeAnnotation':
+      switch (realTypeAnnotation.memberType) {
+        case 'NumberTypeAnnotation':
+          return wrapNullable('double', 'Double');
+        case 'ObjectTypeAnnotation':
+          imports.add('com.facebook.react.bridge.WritableMap');
+          return wrapNullable('WritableMap');
+        case 'StringTypeAnnotation':
+          return wrapNullable('String');
+        default:
+          throw new Error(
+            `Unsupported union member returning value, found: ${realTypeAnnotation.memberType}"`,
+          );
+      }
     case 'ObjectTypeAnnotation':
       imports.add('com.facebook.react.bridge.WritableMap');
       return wrapNullable('WritableMap');
@@ -239,10 +264,7 @@ function translateFunctionReturnTypeToJavaType(
       imports.add('com.facebook.react.bridge.WritableArray');
       return wrapNullable('WritableArray');
     default:
-      (realTypeAnnotation.type:
-        | 'EnumDeclaration'
-        | 'MixedTypeAnnotation'
-        | 'UnionTypeAnnotation');
+      (realTypeAnnotation.type: 'EnumDeclaration' | 'MixedTypeAnnotation');
       throw new Error(createErrorMessage(realTypeAnnotation.type));
   }
 }
@@ -294,6 +316,19 @@ function getFalsyReturnStatementFromReturnType(
         default:
           throw new Error(createErrorMessage(realTypeAnnotation.type));
       }
+    case 'UnionTypeAnnotation':
+      switch (realTypeAnnotation.memberType) {
+        case 'NumberTypeAnnotation':
+          return nullable ? 'return null;' : 'return 0;';
+        case 'ObjectTypeAnnotation':
+          return 'return null;';
+        case 'StringTypeAnnotation':
+          return nullable ? 'return null;' : 'return "";';
+        default:
+          throw new Error(
+            `Unsupported union member returning value, found: ${realTypeAnnotation.memberType}"`,
+          );
+      }
     case 'StringTypeAnnotation':
       return nullable ? 'return null;' : 'return "";';
     case 'ObjectTypeAnnotation':
@@ -303,10 +338,7 @@ function getFalsyReturnStatementFromReturnType(
     case 'ArrayTypeAnnotation':
       return 'return null;';
     default:
-      (realTypeAnnotation.type:
-        | 'EnumDeclaration'
-        | 'MixedTypeAnnotation'
-        | 'UnionTypeAnnotation');
+      (realTypeAnnotation.type: 'EnumDeclaration' | 'MixedTypeAnnotation');
       throw new Error(createErrorMessage(realTypeAnnotation.type));
   }
 }
diff --git a/packages/react-native-codegen/src/generators/modules/GenerateModuleJniCpp.js b/packages/react-native-codegen/src/generators/modules/GenerateModuleJniCpp.js
index 891f4fa6103790..490d6cd630eba2 100644
--- a/packages/react-native-codegen/src/generators/modules/GenerateModuleJniCpp.js
+++ b/packages/react-native-codegen/src/generators/modules/GenerateModuleJniCpp.js
@@ -165,6 +165,19 @@ function translateReturnTypeToKind(
             `Unknown enum prop type for returning value, found: ${realTypeAnnotation.type}"`,
           );
       }
+    case 'UnionTypeAnnotation':
+      switch (typeAnnotation.memberType) {
+        case 'NumberTypeAnnotation':
+          return 'NumberKind';
+        case 'ObjectTypeAnnotation':
+          return 'ObjectKind';
+        case 'StringTypeAnnotation':
+          return 'StringKind';
+        default:
+          throw new Error(
+            `Unsupported union member returning value, found: ${realTypeAnnotation.memberType}"`,
+          );
+      }
     case 'NumberTypeAnnotation':
       return 'NumberKind';
     case 'DoubleTypeAnnotation':
@@ -182,10 +195,7 @@ function translateReturnTypeToKind(
     case 'ArrayTypeAnnotation':
       return 'ArrayKind';
     default:
-      (realTypeAnnotation.type:
-        | 'EnumDeclaration'
-        | 'MixedTypeAnnotation'
-        | 'UnionTypeAnnotation');
+      (realTypeAnnotation.type: 'EnumDeclaration' | 'MixedTypeAnnotation');
       throw new Error(
         `Unknown prop type for returning value, found: ${realTypeAnnotation.type}"`,
       );
@@ -234,6 +244,19 @@ function translateParamTypeToJniType(
             `Unknown enum prop type for method arg, found: ${realTypeAnnotation.type}"`,
           );
       }
+    case 'UnionTypeAnnotation':
+      switch (typeAnnotation.memberType) {
+        case 'NumberTypeAnnotation':
+          return !isRequired ? 'Ljava/lang/Double;' : 'D';
+        case 'ObjectTypeAnnotation':
+          return 'Lcom/facebook/react/bridge/ReadableMap;';
+        case 'StringTypeAnnotation':
+          return 'Ljava/lang/String;';
+        default:
+          throw new Error(
+            `Unsupported union prop value, found: ${realTypeAnnotation.memberType}"`,
+          );
+      }
     case 'NumberTypeAnnotation':
       return !isRequired ? 'Ljava/lang/Double;' : 'D';
     case 'DoubleTypeAnnotation':
@@ -251,10 +274,7 @@ function translateParamTypeToJniType(
     case 'FunctionTypeAnnotation':
       return 'Lcom/facebook/react/bridge/Callback;';
     default:
-      (realTypeAnnotation.type:
-        | 'EnumDeclaration'
-        | 'MixedTypeAnnotation'
-        | 'UnionTypeAnnotation');
+      (realTypeAnnotation.type: 'EnumDeclaration' | 'MixedTypeAnnotation');
       throw new Error(
         `Unknown prop type for method arg, found: ${realTypeAnnotation.type}"`,
       );
@@ -300,6 +320,19 @@ function translateReturnTypeToJniType(
             `Unknown enum prop type for method return type, found: ${realTypeAnnotation.type}"`,
           );
       }
+    case 'UnionTypeAnnotation':
+      switch (typeAnnotation.memberType) {
+        case 'NumberTypeAnnotation':
+          return nullable ? 'Ljava/lang/Double;' : 'D';
+        case 'ObjectTypeAnnotation':
+          return 'Lcom/facebook/react/bridge/WritableMap;';
+        case 'StringTypeAnnotation':
+          return 'Ljava/lang/String;';
+        default:
+          throw new Error(
+            `Unsupported union member type, found: ${realTypeAnnotation.memberType}"`,
+          );
+      }
     case 'NumberTypeAnnotation':
       return nullable ? 'Ljava/lang/Double;' : 'D';
     case 'DoubleTypeAnnotation':
@@ -317,10 +350,7 @@ function translateReturnTypeToJniType(
     case 'ArrayTypeAnnotation':
       return 'Lcom/facebook/react/bridge/WritableArray;';
     default:
-      (realTypeAnnotation.type:
-        | 'EnumDeclaration'
-        | 'MixedTypeAnnotation'
-        | 'UnionTypeAnnotation');
+      (realTypeAnnotation.type: 'EnumDeclaration' | 'MixedTypeAnnotation');
       throw new Error(
         `Unknown prop type for method return type, found: ${realTypeAnnotation.type}"`,
       );
diff --git a/packages/react-native-codegen/src/generators/modules/GenerateModuleObjCpp/serializeMethod.js b/packages/react-native-codegen/src/generators/modules/GenerateModuleObjCpp/serializeMethod.js
index d0864ca5ea8ee2..2894de5ccf262d 100644
--- a/packages/react-native-codegen/src/generators/modules/GenerateModuleObjCpp/serializeMethod.js
+++ b/packages/react-native-codegen/src/generators/modules/GenerateModuleObjCpp/serializeMethod.js
@@ -357,13 +357,25 @@ function getReturnObjCType(
             `Unsupported enum return type for ${methodName}. Found: ${typeAnnotation.type}`,
           );
       }
+    case 'UnionTypeAnnotation':
+      switch (typeAnnotation.memberType) {
+        case 'NumberTypeAnnotation':
+          return wrapIntoNullableIfNeeded('NSNumber *');
+        case 'ObjectTypeAnnotation':
+          return wrapIntoNullableIfNeeded('NSDictionary *');
+        case 'StringTypeAnnotation':
+          // TODO: Can NSString * returns not be _Nullable?
+          // In the legacy codegen, we don't surround NSSTring * with _Nullable
+          return wrapIntoNullableIfNeeded('NSString *');
+        default:
+          throw new Error(
+            `Unsupported union return type for ${methodName}, found: ${typeAnnotation.memberType}"`,
+          );
+      }
     case 'GenericObjectTypeAnnotation':
       return wrapIntoNullableIfNeeded('NSDictionary *');
     default:
-      (typeAnnotation.type:
-        | 'EnumDeclaration'
-        | 'MixedTypeAnnotation'
-        | 'UnionTypeAnnotation');
+      (typeAnnotation.type: 'EnumDeclaration' | 'MixedTypeAnnotation');
       throw new Error(
         `Unsupported return type for ${methodName}. Found: ${typeAnnotation.type}`,
       );
@@ -413,11 +425,21 @@ function getReturnJSType(
             `Unsupported return type for ${methodName}. Found: ${typeAnnotation.type}`,
           );
       }
+    case 'UnionTypeAnnotation':
+      switch (typeAnnotation.memberType) {
+        case 'NumberTypeAnnotation':
+          return 'NumberKind';
+        case 'ObjectTypeAnnotation':
+          return 'ObjectKind';
+        case 'StringTypeAnnotation':
+          return 'StringKind';
+        default:
+          throw new Error(
+            `Unsupported return type for ${methodName}. Found: ${typeAnnotation.type}`,
+          );
+      }
     default:
-      (typeAnnotation.type:
-        | 'EnumDeclaration'
-        | 'MixedTypeAnnotation'
-        | 'UnionTypeAnnotation');
+      (typeAnnotation.type: 'EnumDeclaration' | 'MixedTypeAnnotation');
       throw new Error(
         `Unsupported return type for ${methodName}. Found: ${typeAnnotation.type}`,
       );
diff --git a/packages/react-native-codegen/src/parsers/flow/modules/__test_fixtures__/fixtures.js b/packages/react-native-codegen/src/parsers/flow/modules/__test_fixtures__/fixtures.js
index 151bb480daabfe..3b42068a003ec2 100644
--- a/packages/react-native-codegen/src/parsers/flow/modules/__test_fixtures__/fixtures.js
+++ b/packages/react-native-codegen/src/parsers/flow/modules/__test_fixtures__/fixtures.js
@@ -529,6 +529,35 @@ export default TurboModuleRegistry.getEnforcing<Spec>('SampleTurboModule');
 
 `;
 
+const NATIVE_MODULE_WITH_UNION = `
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ */
+
+'use strict';
+
+import type {TurboModule} from '../RCTExport';
+import * as TurboModuleRegistry from '../TurboModuleRegistry';
+
+export type ChooseInt = 1 | 2 | 3;
+export type ChooseFloat = 1.44 | 2.88 | 5.76;
+export type ChooseObject = {} | {low: string};
+export type ChooseString = 'One' | 'Two' | 'Three';
+
+export interface Spec extends TurboModule {
+ +getUnion: (chooseInt: ChooseInt, chooseFloat: ChooseFloat, chooseObject: ChooseObject, chooseString: ChooseString) => ChooseObject;
+}
+
+export default TurboModuleRegistry.getEnforcing<Spec>('SampleTurboModule');
+
+`;
+
 const ANDROID_ONLY_NATIVE_MODULE = `
 /**
  * Copyright (c) Meta Platforms, Inc. and affiliates.
@@ -671,6 +700,7 @@ module.exports = {
   NATIVE_MODULE_WITH_ARRAY_WITH_ALIAS,
   NATIVE_MODULE_WITH_BASIC_PARAM_TYPES,
   NATIVE_MODULE_WITH_CALLBACK,
+  NATIVE_MODULE_WITH_UNION,
   EMPTY_NATIVE_MODULE,
   ANDROID_ONLY_NATIVE_MODULE,
   IOS_ONLY_NATIVE_MODULE,
diff --git a/packages/react-native-codegen/src/parsers/flow/modules/__tests__/__snapshots__/module-parser-snapshot-test.js.snap b/packages/react-native-codegen/src/parsers/flow/modules/__tests__/__snapshots__/module-parser-snapshot-test.js.snap
index 8f308ace82dca7..32222a962a2213 100644
--- a/packages/react-native-codegen/src/parsers/flow/modules/__tests__/__snapshots__/module-parser-snapshot-test.js.snap
+++ b/packages/react-native-codegen/src/parsers/flow/modules/__tests__/__snapshots__/module-parser-snapshot-test.js.snap
@@ -1628,6 +1628,69 @@ exports[`RN Codegen Flow Parser can generate fixture NATIVE_MODULE_WITH_SIMPLE_O
 }"
 `;
 
+exports[`RN Codegen Flow Parser can generate fixture NATIVE_MODULE_WITH_UNION 1`] = `
+"{
+  'modules': {
+    'NativeSampleTurboModule': {
+      'type': 'NativeModule',
+      'aliases': {},
+      'spec': {
+        'properties': [
+          {
+            'name': 'getUnion',
+            'optional': false,
+            'typeAnnotation': {
+              'type': 'FunctionTypeAnnotation',
+              'returnTypeAnnotation': {
+                'type': 'UnionTypeAnnotation',
+                'memberType': 'ObjectTypeAnnotation'
+              },
+              'params': [
+                {
+                  'name': 'chooseInt',
+                  'optional': false,
+                  'typeAnnotation': {
+                    'type': 'UnionTypeAnnotation',
+                    'memberType': 'NumberTypeAnnotation'
+                  }
+                },
+                {
+                  'name': 'chooseFloat',
+                  'optional': false,
+                  'typeAnnotation': {
+                    'type': 'UnionTypeAnnotation',
+                    'memberType': 'NumberTypeAnnotation'
+                  }
+                },
+                {
+                  'name': 'chooseObject',
+                  'optional': false,
+                  'typeAnnotation': {
+                    'type': 'UnionTypeAnnotation',
+                    'memberType': 'ObjectTypeAnnotation'
+                  }
+                },
+                {
+                  'name': 'chooseString',
+                  'optional': false,
+                  'typeAnnotation': {
+                    'type': 'UnionTypeAnnotation',
+                    'memberType': 'StringTypeAnnotation'
+                  }
+                }
+              ]
+            }
+          }
+        ]
+      },
+      'moduleNames': [
+        'SampleTurboModule'
+      ]
+    }
+  }
+}"
+`;
+
 exports[`RN Codegen Flow Parser can generate fixture NATIVE_MODULE_WITH_UNSAFE_OBJECT 1`] = `
 "{
   'modules': {
diff --git a/packages/react-native-codegen/src/parsers/flow/modules/index.js b/packages/react-native-codegen/src/parsers/flow/modules/index.js
index bc6e28e6573cfd..2755cc5396d7af 100644
--- a/packages/react-native-codegen/src/parsers/flow/modules/index.js
+++ b/packages/react-native-codegen/src/parsers/flow/modules/index.js
@@ -15,8 +15,6 @@ import type {
   NativeModuleAliasMap,
   NativeModuleArrayTypeAnnotation,
   NativeModuleBaseTypeAnnotation,
-  NativeModuleFunctionTypeAnnotation,
-  NativeModuleParamTypeAnnotation,
   NativeModulePropertyShape,
   NativeModuleSchema,
   Nullable,
@@ -55,15 +53,12 @@ const {
 } = require('../../parsers-primitives');
 
 const {
-  UnnamedFunctionParamParserError,
   UnsupportedArrayElementTypeAnnotationParserError,
   UnsupportedTypeAnnotationParserError,
-  UnsupportedObjectPropertyTypeAnnotationParserError,
   IncorrectModuleRegistryCallArgumentTypeParserError,
 } = require('../../errors.js');
 
 const {
-  throwIfUnsupportedFunctionReturnTypeAnnotationParserError,
   throwIfModuleInterfaceNotFound,
   throwIfModuleInterfaceIsMisnamed,
   throwIfUnusedModuleInterfaceParserError,
@@ -73,7 +68,6 @@ const {
   throwIfUntypedModule,
   throwIfModuleTypeIsUnsupported,
   throwIfMoreThanOneModuleInterfaceParserError,
-  throwIfUnsupportedFunctionParamTypeAnnotationParserError,
 } = require('../../error-utils');
 
 const {FlowParser} = require('../parser.js');
@@ -309,15 +303,12 @@ function translateTypeAnnotation(
       );
     }
     case 'UnionTypeAnnotation': {
-      if (cxxOnly) {
-        return emitUnionTypeAnnotation(
-          nullable,
-          hasteModuleName,
-          typeAnnotation,
-          parser,
-        );
-      }
-      // Fallthrough
+      return emitUnionTypeAnnotation(
+        nullable,
+        hasteModuleName,
+        typeAnnotation,
+        parser,
+      );
     }
     case 'MixedTypeAnnotation': {
       if (cxxOnly) {
diff --git a/packages/react-native-codegen/src/parsers/typescript/modules/__test_fixtures__/fixtures.js b/packages/react-native-codegen/src/parsers/typescript/modules/__test_fixtures__/fixtures.js
index 4c2f48f5d2fecc..6e71b23714936d 100644
--- a/packages/react-native-codegen/src/parsers/typescript/modules/__test_fixtures__/fixtures.js
+++ b/packages/react-native-codegen/src/parsers/typescript/modules/__test_fixtures__/fixtures.js
@@ -555,6 +555,32 @@ export interface Spec extends TurboModule {
 export default TurboModuleRegistry.getEnforcing<Spec>('SampleTurboModule');
 `;
 
+const NATIVE_MODULE_WITH_UNION = `
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+import type {TurboModule} from 'react-native/Libraries/TurboModule/RCTExport';
+import * as TurboModuleRegistry from 'react-native/Libraries/TurboModule/TurboModuleRegistry';
+
+export type ChooseInt = 1 | 2 | 3;
+export type ChooseFloat = 1.44 | 2.88 | 5.76;
+export type ChooseObject = {} | {low: string};
+export type ChooseString = 'One' | 'Two' | 'Three';
+
+export interface Spec extends TurboModule {
+  readonly getUnion: (chooseInt: ChooseInt, chooseFloat: ChooseFloat, chooseObject: ChooseObject, chooseString: ChooseString) => ChooseObject;
+}
+
+export default TurboModuleRegistry.getEnforcing<Spec>('SampleTurboModule');
+
+`;
+
 const ANDROID_ONLY_NATIVE_MODULE = `
 /**
  * Copyright (c) Meta Platforms, Inc. and affiliates.
@@ -693,6 +719,7 @@ module.exports = {
   NATIVE_MODULE_WITH_ARRAY2_WITH_ALIAS,
   NATIVE_MODULE_WITH_BASIC_PARAM_TYPES,
   NATIVE_MODULE_WITH_CALLBACK,
+  NATIVE_MODULE_WITH_UNION,
   EMPTY_NATIVE_MODULE,
   ANDROID_ONLY_NATIVE_MODULE,
   IOS_ONLY_NATIVE_MODULE,
diff --git a/packages/react-native-codegen/src/parsers/typescript/modules/__tests__/__snapshots__/typescript-module-parser-snapshot-test.js.snap b/packages/react-native-codegen/src/parsers/typescript/modules/__tests__/__snapshots__/typescript-module-parser-snapshot-test.js.snap
index 185a836a066752..c787dcbcbb0d7e 100644
--- a/packages/react-native-codegen/src/parsers/typescript/modules/__tests__/__snapshots__/typescript-module-parser-snapshot-test.js.snap
+++ b/packages/react-native-codegen/src/parsers/typescript/modules/__tests__/__snapshots__/typescript-module-parser-snapshot-test.js.snap
@@ -1835,6 +1835,69 @@ exports[`RN Codegen TypeScript Parser can generate fixture NATIVE_MODULE_WITH_SI
 }"
 `;
 
+exports[`RN Codegen TypeScript Parser can generate fixture NATIVE_MODULE_WITH_UNION 1`] = `
+"{
+  'modules': {
+    'NativeSampleTurboModule': {
+      'type': 'NativeModule',
+      'aliases': {},
+      'spec': {
+        'properties': [
+          {
+            'name': 'getUnion',
+            'optional': false,
+            'typeAnnotation': {
+              'type': 'FunctionTypeAnnotation',
+              'returnTypeAnnotation': {
+                'type': 'UnionTypeAnnotation',
+                'memberType': 'ObjectTypeAnnotation'
+              },
+              'params': [
+                {
+                  'name': 'chooseInt',
+                  'optional': false,
+                  'typeAnnotation': {
+                    'type': 'UnionTypeAnnotation',
+                    'memberType': 'NumberTypeAnnotation'
+                  }
+                },
+                {
+                  'name': 'chooseFloat',
+                  'optional': false,
+                  'typeAnnotation': {
+                    'type': 'UnionTypeAnnotation',
+                    'memberType': 'NumberTypeAnnotation'
+                  }
+                },
+                {
+                  'name': 'chooseObject',
+                  'optional': false,
+                  'typeAnnotation': {
+                    'type': 'UnionTypeAnnotation',
+                    'memberType': 'ObjectTypeAnnotation'
+                  }
+                },
+                {
+                  'name': 'chooseString',
+                  'optional': false,
+                  'typeAnnotation': {
+                    'type': 'UnionTypeAnnotation',
+                    'memberType': 'StringTypeAnnotation'
+                  }
+                }
+              ]
+            }
+          }
+        ]
+      },
+      'moduleNames': [
+        'SampleTurboModule'
+      ]
+    }
+  }
+}"
+`;
+
 exports[`RN Codegen TypeScript Parser can generate fixture NATIVE_MODULE_WITH_UNSAFE_OBJECT 1`] = `
 "{
   'modules': {
diff --git a/packages/react-native-codegen/src/parsers/typescript/modules/index.js b/packages/react-native-codegen/src/parsers/typescript/modules/index.js
index 5df5fcbfb0a8d9..2d811c02e21e7a 100644
--- a/packages/react-native-codegen/src/parsers/typescript/modules/index.js
+++ b/packages/react-native-codegen/src/parsers/typescript/modules/index.js
@@ -140,6 +140,18 @@ function translateArrayTypeAnnotation(
       );
     }
 
+    // TODO: Added as a work-around for now until TupleTypeAnnotation are fully supported in both flow and TS
+    // Right now they are partially treated as UnionTypeAnnotation
+    if (elementType.type === 'UnionTypeAnnotation') {
+      throw new UnsupportedArrayElementTypeAnnotationParserError(
+        hasteModuleName,
+        tsElementType,
+        tsArrayType,
+        'UnionTypeAnnotation',
+        language,
+      );
+    }
+
     const finalTypeAnnotation: NativeModuleArrayTypeAnnotation<
       Nullable<NativeModuleBaseTypeAnnotation>,
     > = {
@@ -314,15 +326,12 @@ function translateTypeAnnotation(
       );
     }
     case 'TSUnionType': {
-      if (cxxOnly) {
-        return emitUnionTypeAnnotation(
-          nullable,
-          hasteModuleName,
-          typeAnnotation,
-          parser,
-        );
-      }
-      // Fallthrough
+      return emitUnionTypeAnnotation(
+        nullable,
+        hasteModuleName,
+        typeAnnotation,
+        parser,
+      );
     }
     case 'TSUnknownKeyword': {
       if (cxxOnly) {