googleapis
diff --git a/google/api_core/path_template.py b/google/api_core/path_template.py
@@ -298,6 +298,26 @@ def transcode(http_options, message=None, **request_kwargs):
         # Assign body and query params
         body = http_option.get("body")
 
+        # gapic-generator-python appends an underscore to field names
+        # that collide with python keywords. See related issue
+        # https://github.com/googleapis/python-api-core/issues/227
+        # Make sure that when the fields are REST encoded, the
+        # Python-specific trailing underscore is removed before going on the wire.
+        # `leftovers` can either be a dict or protobuf message.
+        # When `leftovers` is a dict, the `_` suffix in each key
+        # is stripped away as it is not possible to natively define a field
+        # with a trailing underscore in protobuf.
+        # When `leftovers` is a protobuf message, we need to use an underscore
+        # suffix when accessing the field in the protobuf message when the
+        # field has an underscore suffix.
+        field_suffix = ""
+
+        if isinstance(leftovers, dict):
+            leftovers = {key.rstrip("_"): val for key, val in leftovers.items()}
+        elif body:
+            if hasattr(leftovers, body + "_"):
+                field_suffix = "_"
+
         if body:
             if body == "*":
                 request["body"] = leftovers
@@ -308,8 +328,8 @@ def transcode(http_options, message=None, **request_kwargs):
             else:
                 try:
                     if message:
-                        request["body"] = getattr(leftovers, body)
-                        delete_field(leftovers, body)
+                        request["body"] = getattr(leftovers, f"{body}{field_suffix}")
+                        delete_field(leftovers, f"{body}{field_suffix}")
                     else:
                         request["body"] = leftovers.pop(body)
                 except (KeyError, AttributeError):

diff --git a/tests/unit/test_path_template.py b/tests/unit/test_path_template.py
@@ -17,10 +17,22 @@
 import mock
 import pytest
 
+import proto
+
 from google.api import auth_pb2
 from google.api_core import path_template
 
 
+class Breakpoint(proto.Message):
+    name = proto.Field(proto.STRING, number=1)
+
+
+class SomeMessage(proto.Message):
+    breakpoint_ = proto.Field(Breakpoint, number=1)
+    debuggee_id = proto.Field(proto.STRING, number=2)
+    stacktrace_ = proto.Field(proto.STRING, number=3)
+
+
 @pytest.mark.parametrize(
     "tmpl, args, kwargs, expected_result",
     [
@@ -413,6 +425,27 @@ def test_transcode_with_wildcard(
             {"data": {"id": 1, "info": "some info"}, "foo": "bar"},
             ["post", "/v1/no/template", {"id": 1, "info": "some info"}, {"foo": "bar"}],
         ],
+        # Single field body with trailing underscore
+        [
+            [["post", "/v1/no/template", "data"]],
+            None,
+            {"data": {"id": 1, "info": "some info"}, "foo_": "bar"},
+            ["post", "/v1/no/template", {"id": 1, "info": "some info"}, {"foo": "bar"}],
+        ],
+        # Single field body with reserved keyword, using message where field name has trailing underscore
+        [
+            [["post", "/v1/no/template", "breakpoint"]],
+            SomeMessage(
+                breakpoint_=Breakpoint(name="foo"), debuggee_id="bar", stacktrace_="baz"
+            )._pb,
+            {},
+            [
+                "post",
+                "/v1/no/template",
+                Breakpoint(name="foo")._pb,
+                SomeMessage(debuggee_id="bar", stacktrace_="baz")._pb,
+            ],
+        ],
         [
             [["post", "/v1/no/template", "oauth"]],
             auth_pb2.AuthenticationRule(