diff --git a/google/cloud/spanner_v1/types/transaction.py b/google/cloud/spanner_v1/types/transaction.py
index f6c24708a2..0c7cb06bf0 100644
--- a/google/cloud/spanner_v1/types/transaction.py
+++ b/google/cloud/spanner_v1/types/transaction.py
@@ -401,8 +401,25 @@ class ReadWrite(proto.Message):
         r"""Message type to initiate a read-write transaction. Currently
         this transaction type has no options.
 
+        Attributes:
+            read_lock_mode (google.cloud.spanner_v1.types.TransactionOptions.ReadWrite.ReadLockMode):
+                Read lock mode for the transaction.
         """
 
+        class ReadLockMode(proto.Enum):
+            r"""``ReadLockMode`` is used to set the read lock mode for read-write
+            transactions.
+            """
+            READ_LOCK_MODE_UNSPECIFIED = 0
+            PESSIMISTIC = 1
+            OPTIMISTIC = 2
+
+        read_lock_mode = proto.Field(
+            proto.ENUM,
+            number=1,
+            enum="TransactionOptions.ReadWrite.ReadLockMode",
+        )
+
     class PartitionedDml(proto.Message):
         r"""Message type to initiate a Partitioned DML transaction."""
 
diff --git a/tests/unit/gapic/spanner_v1/test_spanner.py b/tests/unit/gapic/spanner_v1/test_spanner.py
index d17741419e..0e70b5119a 100644
--- a/tests/unit/gapic/spanner_v1/test_spanner.py
+++ b/tests/unit/gapic/spanner_v1/test_spanner.py
@@ -2926,7 +2926,11 @@ def test_begin_transaction_flattened():
         # using the keyword arguments to the method.
         client.begin_transaction(
             session="session_value",
-            options=transaction.TransactionOptions(read_write=None),
+            options=transaction.TransactionOptions(
+                read_write=transaction.TransactionOptions.ReadWrite(
+                    read_lock_mode=transaction.TransactionOptions.ReadWrite.ReadLockMode.PESSIMISTIC
+                )
+            ),
         )
 
         # Establish that the underlying call was made with the expected
@@ -2937,7 +2941,11 @@ def test_begin_transaction_flattened():
         mock_val = "session_value"
         assert arg == mock_val
         arg = args[0].options
-        mock_val = transaction.TransactionOptions(read_write=None)
+        mock_val = transaction.TransactionOptions(
+            read_write=transaction.TransactionOptions.ReadWrite(
+                read_lock_mode=transaction.TransactionOptions.ReadWrite.ReadLockMode.PESSIMISTIC
+            )
+        )
         assert arg == mock_val
 
 
@@ -2952,7 +2960,11 @@ def test_begin_transaction_flattened_error():
         client.begin_transaction(
             spanner.BeginTransactionRequest(),
             session="session_value",
-            options=transaction.TransactionOptions(read_write=None),
+            options=transaction.TransactionOptions(
+                read_write=transaction.TransactionOptions.ReadWrite(
+                    read_lock_mode=transaction.TransactionOptions.ReadWrite.ReadLockMode.PESSIMISTIC
+                )
+            ),
         )
 
 
@@ -2976,7 +2988,11 @@ async def test_begin_transaction_flattened_async():
         # using the keyword arguments to the method.
         response = await client.begin_transaction(
             session="session_value",
-            options=transaction.TransactionOptions(read_write=None),
+            options=transaction.TransactionOptions(
+                read_write=transaction.TransactionOptions.ReadWrite(
+                    read_lock_mode=transaction.TransactionOptions.ReadWrite.ReadLockMode.PESSIMISTIC
+                )
+            ),
         )
 
         # Establish that the underlying call was made with the expected
@@ -2987,7 +3003,11 @@ async def test_begin_transaction_flattened_async():
         mock_val = "session_value"
         assert arg == mock_val
         arg = args[0].options
-        mock_val = transaction.TransactionOptions(read_write=None)
+        mock_val = transaction.TransactionOptions(
+            read_write=transaction.TransactionOptions.ReadWrite(
+                read_lock_mode=transaction.TransactionOptions.ReadWrite.ReadLockMode.PESSIMISTIC
+            )
+        )
         assert arg == mock_val
 
 
@@ -3003,7 +3023,11 @@ async def test_begin_transaction_flattened_error_async():
         await client.begin_transaction(
             spanner.BeginTransactionRequest(),
             session="session_value",
-            options=transaction.TransactionOptions(read_write=None),
+            options=transaction.TransactionOptions(
+                read_write=transaction.TransactionOptions.ReadWrite(
+                    read_lock_mode=transaction.TransactionOptions.ReadWrite.ReadLockMode.PESSIMISTIC
+                )
+            ),
         )
 
 
@@ -3168,7 +3192,11 @@ def test_commit_flattened():
             mutations=[
                 mutation.Mutation(insert=mutation.Mutation.Write(table="table_value"))
             ],
-            single_use_transaction=transaction.TransactionOptions(read_write=None),
+            single_use_transaction=transaction.TransactionOptions(
+                read_write=transaction.TransactionOptions.ReadWrite(
+                    read_lock_mode=transaction.TransactionOptions.ReadWrite.ReadLockMode.PESSIMISTIC
+                )
+            ),
         )
 
         # Establish that the underlying call was made with the expected
@@ -3184,7 +3212,9 @@ def test_commit_flattened():
         ]
         assert arg == mock_val
         assert args[0].single_use_transaction == transaction.TransactionOptions(
-            read_write=None
+            read_write=transaction.TransactionOptions.ReadWrite(
+                read_lock_mode=transaction.TransactionOptions.ReadWrite.ReadLockMode.PESSIMISTIC
+            )
         )
 
 
@@ -3203,7 +3233,11 @@ def test_commit_flattened_error():
             mutations=[
                 mutation.Mutation(insert=mutation.Mutation.Write(table="table_value"))
             ],
-            single_use_transaction=transaction.TransactionOptions(read_write=None),
+            single_use_transaction=transaction.TransactionOptions(
+                read_write=transaction.TransactionOptions.ReadWrite(
+                    read_lock_mode=transaction.TransactionOptions.ReadWrite.ReadLockMode.PESSIMISTIC
+                )
+            ),
         )
 
 
@@ -3229,7 +3263,11 @@ async def test_commit_flattened_async():
             mutations=[
                 mutation.Mutation(insert=mutation.Mutation.Write(table="table_value"))
             ],
-            single_use_transaction=transaction.TransactionOptions(read_write=None),
+            single_use_transaction=transaction.TransactionOptions(
+                read_write=transaction.TransactionOptions.ReadWrite(
+                    read_lock_mode=transaction.TransactionOptions.ReadWrite.ReadLockMode.PESSIMISTIC
+                )
+            ),
         )
 
         # Establish that the underlying call was made with the expected
@@ -3245,7 +3283,9 @@ async def test_commit_flattened_async():
         ]
         assert arg == mock_val
         assert args[0].single_use_transaction == transaction.TransactionOptions(
-            read_write=None
+            read_write=transaction.TransactionOptions.ReadWrite(
+                read_lock_mode=transaction.TransactionOptions.ReadWrite.ReadLockMode.PESSIMISTIC
+            )
         )
 
 
@@ -3265,7 +3305,11 @@ async def test_commit_flattened_error_async():
             mutations=[
                 mutation.Mutation(insert=mutation.Mutation.Write(table="table_value"))
             ],
-            single_use_transaction=transaction.TransactionOptions(read_write=None),
+            single_use_transaction=transaction.TransactionOptions(
+                read_write=transaction.TransactionOptions.ReadWrite(
+                    read_lock_mode=transaction.TransactionOptions.ReadWrite.ReadLockMode.PESSIMISTIC
+                )
+            ),
         )