diff --git a/pymongo/bulk.py b/pymongo/bulk.py
index 0f5730928..829b482c9 100644
--- a/pymongo/bulk.py
+++ b/pymongo/bulk.py
@@ -267,17 +267,18 @@ class _Bulk(object):
         # sock_info.write_command.
         sock_info.validate_session(client, session)
         while run:
-            cmd = SON([(_COMMANDS[run.op_type], self.collection.name),
-                       ('ordered', self.ordered)])
-            if not write_concern.is_server_default:
-                cmd['writeConcern'] = write_concern.document
-            if self.bypass_doc_val:
-                cmd['bypassDocumentValidation'] = True
+            cmd_name = _COMMANDS[run.op_type]
             bwc = self.bulk_ctx_class(
-                db_name, cmd, sock_info, op_id, listeners, session,
+                db_name, cmd_name, sock_info, op_id, listeners, session,
                 run.op_type, self.collection.codec_options)
 
             while run.idx_offset < len(run.ops):
+                cmd = SON([(cmd_name, self.collection.name),
+                           ('ordered', self.ordered)])
+                if not write_concern.is_server_default:
+                    cmd['writeConcern'] = write_concern.document
+                if self.bypass_doc_val:
+                    cmd['bypassDocumentValidation'] = True
                 if session:
                     # Start a new retryable write unless one was already
                     # started for this command.
@@ -287,9 +288,10 @@ class _Bulk(object):
                     session._apply_to(cmd, retryable, ReadPreference.PRIMARY,
                                       sock_info)
                 sock_info.send_cluster_time(cmd, session, client)
+                sock_info.add_server_api(cmd)
                 ops = islice(run.ops, run.idx_offset, None)
                 # Run as many ops as possible in one command.
-                result, to_send = bwc.execute(ops, client)
+                result, to_send = bwc.execute(cmd, ops, client)
 
                 # Retryable writeConcernErrors halt the execution of this run.
                 wce = result.get('writeConcernError', {})
@@ -359,17 +361,19 @@ class _Bulk(object):
         run = self.current_run
 
         while run:
-            cmd = SON([(_COMMANDS[run.op_type], self.collection.name),
-                       ('ordered', False),
-                       ('writeConcern', {'w': 0})])
+            cmd_name = _COMMANDS[run.op_type]
             bwc = self.bulk_ctx_class(
-                db_name, cmd, sock_info, op_id, listeners, None,
+                db_name, cmd_name, sock_info, op_id, listeners, None,
                 run.op_type, self.collection.codec_options)
 
             while run.idx_offset < len(run.ops):
+                cmd = SON([(cmd_name, self.collection.name),
+                           ('ordered', False),
+                           ('writeConcern', {'w': 0})])
+                sock_info.add_server_api(cmd)
                 ops = islice(run.ops, run.idx_offset, None)
                 # Run as many ops as possible.
-                to_send = bwc.execute_unack(ops, client)
+                to_send = bwc.execute_unack(cmd, ops, client)
                 run.idx_offset += len(to_send)
             self.current_run = run = next(generator, None)
 
diff --git a/pymongo/message.py b/pymongo/message.py
index 8a496d5b1..86a83f152 100644
--- a/pymongo/message.py
+++ b/pymongo/message.py
@@ -704,50 +704,48 @@ def _get_more(collection_name, num_to_return, cursor_id, ctx=None):
 class _BulkWriteContext(object):
     """A wrapper around SocketInfo for use with write splitting functions."""
 
-    __slots__ = ('db_name', 'command', 'sock_info', 'op_id',
+    __slots__ = ('db_name', 'sock_info', 'op_id',
                  'name', 'field', 'publish', 'start_time', 'listeners',
                  'session', 'compress', 'op_type', 'codec')
 
-    def __init__(self, database_name, command, sock_info, operation_id,
+    def __init__(self, database_name, cmd_name, sock_info, operation_id,
                  listeners, session, op_type, codec):
         self.db_name = database_name
-        self.command = command
         self.sock_info = sock_info
         self.op_id = operation_id
         self.listeners = listeners
         self.publish = listeners.enabled_for_commands
-        self.name = next(iter(command))
+        self.name = cmd_name
         self.field = _FIELD_MAP[self.name]
         self.start_time = datetime.datetime.now() if self.publish else None
         self.session = session
         self.compress = True if sock_info.compression_context else False
         self.op_type = op_type
         self.codec = codec
-        sock_info.add_server_api(command)
 
-    def _batch_command(self, docs):
+    def _batch_command(self, cmd, docs):
         namespace = self.db_name + '.$cmd'
         request_id, msg, to_send = _do_batched_op_msg(
-            namespace, self.op_type, self.command, docs, self.check_keys,
+            namespace, self.op_type, cmd, docs, self.check_keys,
             self.codec, self)
         if not to_send:
             raise InvalidOperation("cannot do an empty bulk write")
         return request_id, msg, to_send
 
-    def execute(self, docs, client):
-        request_id, msg, to_send = self._batch_command(docs)
-        result = self.write_command(request_id, msg, to_send)
+    def execute(self, cmd, docs, client):
+        request_id, msg, to_send = self._batch_command(cmd, docs)
+        result = self.write_command(cmd, request_id, msg, to_send)
         client._process_response(result, self.session)
         return result, to_send
 
-    def execute_unack(self, docs, client):
-        request_id, msg, to_send = self._batch_command(docs)
+    def execute_unack(self, cmd, docs, client):
+        request_id, msg, to_send = self._batch_command(cmd, docs)
         # Though this isn't strictly a "legacy" write, the helper
         # handles publishing commands and sending our message
         # without receiving a result. Send 0 for max_doc_size
         # to disable size checking. Size checking is handled while
         # the documents are encoded to BSON.
-        self.unack_write(request_id, msg, 0, to_send)
+        self.unack_write(cmd, request_id, msg, 0, to_send)
         return to_send
 
     @property
@@ -778,12 +776,12 @@ class _BulkWriteContext(object):
         """The maximum size of a BSON command before batch splitting."""
         return self.max_bson_size
 
-    def unack_write(self, request_id, msg, max_doc_size, docs):
+    def unack_write(self, cmd, request_id, msg, max_doc_size, docs):
         """A proxy for SocketInfo.unack_write that handles event publishing.
         """
         if self.publish:
             duration = datetime.datetime.now() - self.start_time
-            cmd = self._start(request_id, docs)
+            cmd = self._start(cmd, request_id, docs)
             start = datetime.datetime.now()
         try:
             result = self.sock_info.unack_write(msg, max_doc_size)
@@ -811,12 +809,12 @@ class _BulkWriteContext(object):
             self.start_time = datetime.datetime.now()
         return result
 
-    def write_command(self, request_id, msg, docs):
+    def write_command(self, cmd, request_id, msg, docs):
         """A proxy for SocketInfo.write_command that handles event publishing.
         """
         if self.publish:
             duration = datetime.datetime.now() - self.start_time
-            self._start(request_id, docs)
+            self._start(cmd, request_id, docs)
             start = datetime.datetime.now()
         try:
             reply = self.sock_info.write_command(request_id, msg)
@@ -836,9 +834,8 @@ class _BulkWriteContext(object):
             self.start_time = datetime.datetime.now()
         return reply
 
-    def _start(self, request_id, docs):
+    def _start(self, cmd, request_id, docs):
         """Publish a CommandStartedEvent."""
-        cmd = self.command.copy()
         cmd[self.field] = docs
         self.listeners.publish_command_start(
             cmd, self.db_name,
@@ -871,10 +868,10 @@ _MAX_SPLIT_SIZE_ENC = 2097152
 class _EncryptedBulkWriteContext(_BulkWriteContext):
     __slots__ = ()
 
-    def _batch_command(self, docs):
+    def _batch_command(self, cmd, docs):
         namespace = self.db_name + '.$cmd'
         msg, to_send = _encode_batched_write_command(
-            namespace, self.op_type, self.command, docs, self.check_keys,
+            namespace, self.op_type, cmd, docs, self.check_keys,
             self.codec, self)
         if not to_send:
             raise InvalidOperation("cannot do an empty bulk write")
@@ -885,17 +882,18 @@ class _EncryptedBulkWriteContext(_BulkWriteContext):
                             DEFAULT_RAW_BSON_OPTIONS)
         return cmd, to_send
 
-    def execute(self, docs, client):
-        cmd, to_send = self._batch_command(docs)
+    def execute(self, cmd, docs, client):
+        batched_cmd, to_send = self._batch_command(cmd, docs)
         result = self.sock_info.command(
-            self.db_name, cmd, codec_options=_UNICODE_REPLACE_CODEC_OPTIONS,
+            self.db_name, batched_cmd,
+            codec_options=_UNICODE_REPLACE_CODEC_OPTIONS,
             session=self.session, client=client)
         return result, to_send
 
-    def execute_unack(self, docs, client):
-        cmd, to_send = self._batch_command(docs)
+    def execute_unack(self, cmd, docs, client):
+        batched_cmd, to_send = self._batch_command(cmd, docs)
         self.sock_info.command(
-            self.db_name, cmd, write_concern=WriteConcern(w=0),
+            self.db_name, batched_cmd, write_concern=WriteConcern(w=0),
             session=self.session, client=client)
         return to_send
 
diff --git a/test/test_transactions.py b/test/test_transactions.py
index 33a9186e8..de3066303 100644
--- a/test/test_transactions.py
+++ b/test/test_transactions.py
@@ -286,6 +286,36 @@ class TestTransactions(TransactionsBase):
                 ):
                     op(*args, session=s)
 
+    # Require 4.2+ for large (16MB+) transactions.
+    @client_context.require_version_min(4, 2)
+    @client_context.require_transactions
+    def test_transaction_starts_with_batched_write(self):
+        # Start a transaction with a batch of operations that needs to be
+        # split.
+        listener = OvertCommandListener()
+        client = rs_client(event_listeners=[listener])
+        coll = client[self.db.name].test
+        coll.delete_many({})
+        listener.reset()
+        self.addCleanup(client.close)
+        self.addCleanup(coll.drop)
+        ops = [InsertOne({'a': '1'*(10*1024*1024)}) for _ in range(10)]
+        with client.start_session() as session:
+            with session.start_transaction():
+                coll.bulk_write(ops, session=session)
+        # Assert commands were constructed properly.
+        self.assertEqual(['insert', 'insert', 'insert', 'commitTransaction'],
+                         listener.started_command_names())
+        first_cmd = listener.results['started'][0].command
+        self.assertTrue(first_cmd['startTransaction'])
+        lsid = first_cmd['lsid']
+        txn_number = first_cmd['txnNumber']
+        for event in listener.results['started'][1:]:
+            self.assertNotIn('startTransaction', event.command)
+            self.assertEqual(lsid, event.command['lsid'])
+            self.assertEqual(txn_number, event.command['txnNumber'])
+        self.assertEqual(10, coll.count_documents({}))
+
 
 class PatchSessionTimeout(object):
     """Patches the client_session's with_transaction timeout for testing."""