diff --git a/src/auth/token-verifier.ts b/src/auth/token-verifier.ts
index 05566205b5..73fc8f678c 100644
--- a/src/auth/token-verifier.ts
+++ b/src/auth/token-verifier.ts
@@ -529,13 +529,19 @@ export class FirebaseTokenVerifier {
       errorMessage = `${this.tokenInfo.jwtName} has incorrect "iss" (issuer) claim. Expected ` +
         `"${this.issuer}` + projectId + '" but got "' +
         payload.iss + '".' + projectIdMatchMessage + verifyJwtTokenDocsMessage;
-    } else if (typeof payload.sub !== 'string') {
-      errorMessage = `${this.tokenInfo.jwtName} has no "sub" (subject) claim.` + verifyJwtTokenDocsMessage;
-    } else if (payload.sub === '') {
-      errorMessage = `${this.tokenInfo.jwtName} has an empty string "sub" (subject) claim.` + verifyJwtTokenDocsMessage;
-    } else if (payload.sub.length > 128) {
-      errorMessage = `${this.tokenInfo.jwtName} has "sub" (subject) claim longer than 128 characters.` +
-        verifyJwtTokenDocsMessage;
+    } else if (!(payload.event_type !== undefined &&
+      (payload.event_type === 'beforeSendSms' || payload.event_type === 'beforeSendEmail'))) {
+      // excluding `beforeSendSms` and `beforeSendEmail` from processing `sub` as there is no user record available.
+      // `sub` is the same as `uid` which is part of the user record.
+      if (typeof payload.sub !== 'string') {
+        errorMessage = `${this.tokenInfo.jwtName} has no "sub" (subject) claim.` + verifyJwtTokenDocsMessage;
+      } else if (payload.sub === '') {
+        errorMessage = `${this.tokenInfo.jwtName} has an empty "sub" (subject) claim.` +
+          verifyJwtTokenDocsMessage;
+      } else if (payload.sub.length > 128) {
+        errorMessage = `${this.tokenInfo.jwtName} has a "sub" (subject) claim longer than 128 characters.` +
+          verifyJwtTokenDocsMessage;
+      }
     }
     if (errorMessage) {
       throw new FirebaseAuthError(AuthClientErrorCode.INVALID_ARGUMENT, errorMessage);
diff --git a/test/unit/auth/token-verifier.spec.ts b/test/unit/auth/token-verifier.spec.ts
index 7abda8eb08..2d01678ef7 100644
--- a/test/unit/auth/token-verifier.spec.ts
+++ b/test/unit/auth/token-verifier.spec.ts
@@ -341,7 +341,8 @@ describe('FirebaseTokenVerifier', () => {
         });
 
         return tokenVerifier.verifyJWT(mockIdToken)
-          .should.eventually.be.rejectedWith('Firebase ID token has "sub" (subject) claim longer than 128 characters');
+          .should.eventually.be.rejectedWith('Firebase ID token has a "sub" (subject) claim longer than 128 ' +
+          'characters');
       });
     });
 
@@ -659,7 +660,7 @@ describe('FirebaseTokenVerifier', () => {
 
         return authBlockingTokenVerifier._verifyAuthBlockingToken(mockAuthBlockingToken, false, undefined)
           .should.eventually.be.rejectedWith(
-            'Firebase Auth Blocking token has "sub" (subject) claim longer than 128 characters');
+            'Firebase Auth Blocking token has a "sub" (subject) claim longer than 128 characters');
       });
     });
 
@@ -780,5 +781,41 @@ describe('FirebaseTokenVerifier', () => {
       await authBlockingTokenVerifier._verifyAuthBlockingToken(idTokenNoHeader, false, undefined)
         .should.eventually.be.rejectedWith('Firebase Auth Blocking token has no "kid" claim.');
     });
+
+    const eventTypesWithoutUid = ['beforeSendSms', 'beforeSendEmail'];
+    eventTypesWithoutUid.forEach((eventType) => {
+      it('should not throw error on invalid `sub` when event_type is "' + eventType + '"' , async () => {
+        const verifierStub = sinon.stub(PublicKeySignatureVerifier.prototype, 'verify')
+          .resolves();
+        stubs.push(verifierStub);
+
+        const mockAuthBlockingToken = mocks.generateAuthBlockingToken({
+          subject: ''
+        }, {
+          event_type: eventType,
+        });
+        return authBlockingTokenVerifier._verifyAuthBlockingToken(mockAuthBlockingToken, false, undefined)
+          .should.eventually.be.fulfilled;
+      });
+    });
+
+    const eventTypesWithUid = ['beforeCreate', 'beforeSignIn', undefined];
+    eventTypesWithUid.forEach((eventType) => {
+      it('should not throw error on invalid `sub` when event_type is "' + eventType + '"', async () => {
+        const verifierStub = sinon.stub(PublicKeySignatureVerifier.prototype, 'verify')
+          .resolves();
+        stubs.push(verifierStub);
+
+        const mockAuthBlockingToken = mocks.generateAuthBlockingToken({
+          subject: ''
+        }, {
+          event_type: eventType,
+        });
+        return authBlockingTokenVerifier._verifyAuthBlockingToken(mockAuthBlockingToken, false, undefined)
+          .should.eventually.be.rejectedWith('Firebase Auth Blocking token has an empty "sub" (subject) claim.' +
+          ' See https://cloud.google.com/identity-platform/docs/blocking-functions for details on how to retrieve an' +
+          ' Auth Blocking token.');
+      });
+    });
   });
 });