diff --git a/pc/BUILD.gn b/pc/BUILD.gn
index 10c5c7b7ab..84aba07764 100644
--- a/pc/BUILD.gn
+++ b/pc/BUILD.gn
@@ -803,6 +803,7 @@ if (rtc_include_tests) {
       "../rtc_base:rtc_base_tests_utils",
       "../rtc_base/third_party/sigslot",
       "../system_wrappers:metrics",
+      "../test:field_trial",
       "../test:test_main",
       "../test:test_support",
       "//third_party/abseil-cpp/absl/algorithm:container",
diff --git a/pc/media_session.cc b/pc/media_session.cc
index cbff21635e..6d8a9a4891 100644
--- a/pc/media_session.cc
+++ b/pc/media_session.cc
@@ -36,6 +36,7 @@
 #include "rtc_base/logging.h"
 #include "rtc_base/third_party/base64/base64.h"
 #include "rtc_base/unique_id_generator.h"
+#include "system_wrappers/include/field_trial.h"
 
 namespace {
 
@@ -336,6 +337,12 @@ static StreamParams CreateStreamParamsForNewSenderWithSsrcs(
            "a single media streams. This session has multiple "
            "media streams however, so no FlexFEC SSRC will be generated.";
   }
+  if (include_flexfec_stream &&
+      !webrtc::field_trial::IsEnabled("WebRTC-FlexFEC-03")) {
+    include_flexfec_stream = false;
+    RTC_LOG(LS_WARNING)
+        << "WebRTC-FlexFEC trial is not enabled, not sending FlexFEC";
+  }
 
   result.GenerateSsrcs(sender.num_sim_layers, include_rtx_streams,
                        include_flexfec_stream, ssrc_generator);
diff --git a/pc/media_session_unittest.cc b/pc/media_session_unittest.cc
index 5a9002bc4e..d8cb1591a9 100644
--- a/pc/media_session_unittest.cc
+++ b/pc/media_session_unittest.cc
@@ -34,6 +34,7 @@
 #include "rtc_base/ssl_adapter.h"
 #include "rtc_base/strings/string_builder.h"
 #include "rtc_base/unique_id_generator.h"
+#include "test/field_trial.h"
 #include "test/gmock.h"
 
 #define ASSERT_CRYPTO(cd, s, cs)      \
@@ -3456,8 +3457,10 @@ TEST_F(MediaSessionDescriptionFactoryTest, SimSsrcsGenerateMultipleRtxSsrcs) {
 }
 
 // Test that, when the FlexFEC codec is added, a FlexFEC ssrc is created
-// together with a FEC-FR grouping.
+// together with a FEC-FR grouping. Guarded by WebRTC-FlexFEC-03 trial.
 TEST_F(MediaSessionDescriptionFactoryTest, GenerateFlexfecSsrc) {
+  webrtc::test::ScopedFieldTrials override_field_trials(
+      "WebRTC-FlexFEC-03/Enabled/");
   MediaSessionOptions opts;
   AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
                              RtpTransceiverDirection::kSendRecv, kActive,
@@ -3499,6 +3502,8 @@ TEST_F(MediaSessionDescriptionFactoryTest, GenerateFlexfecSsrc) {
 // TODO(brandtr): Remove this test when we support simulcast, either through
 // multiple FlexfecSenders, or through multistream protection.
 TEST_F(MediaSessionDescriptionFactoryTest, SimSsrcsGenerateNoFlexfecSsrcs) {
+  webrtc::test::ScopedFieldTrials override_field_trials(
+      "WebRTC-FlexFEC-03/Enabled/");
   MediaSessionOptions opts;
   AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
                              RtpTransceiverDirection::kSendRecv, kActive,