diff --git a/slack/web/__init__.py b/slack/web/__init__.py
index e69de29bb..3631743b4 100644
--- a/slack/web/__init__.py
+++ b/slack/web/__init__.py
@@ -0,0 +1,28 @@
+import os
+import warnings
+
+# https://api.slack.com/changelog/2020-01-deprecating-antecedents-to-the-conversations-api
+deprecated_method_prefixes_2020_01 = ["channels.", "groups.", "im.", "mpim."]
+
+
+def show_2020_01_deprecation(method_name: str):
+    skip_deprecation = os.environ.get(
+        "SLACKCLIENT_SKIP_DEPRECATION"
+    )  # for unit tests etc.
+    if skip_deprecation:
+        return
+    if not method_name:
+        return
+
+    matched_prefixes = [
+        prefix
+        for prefix in deprecated_method_prefixes_2020_01
+        if method_name.startswith(prefix)
+    ]
+    if len(matched_prefixes) > 0:
+        message = (
+            f"{method_name} is deprecated. Please use the Conversations API instead. "
+            "For more info, go to "
+            "https://api.slack.com/changelog/2020-01-deprecating-antecedents-to-the-conversations-api"
+        )
+        warnings.warn(message)
diff --git a/slack/web/base_client.py b/slack/web/base_client.py
index 2b1201ec8..093a3b6b4 100644
--- a/slack/web/base_client.py
+++ b/slack/web/base_client.py
@@ -15,6 +15,7 @@
 from aiohttp import FormData, BasicAuth
 
 # Internal Imports
+from slack.web import show_2020_01_deprecation
 from slack.web.slack_response import SlackResponse
 import slack.version as ver
 import slack.errors as err
@@ -170,6 +171,7 @@ def api_call(
         if self._event_loop is None:
             self._event_loop = self._get_event_loop()
 
+        show_2020_01_deprecation(api_method)
         future = asyncio.ensure_future(
             self._send(http_verb=http_verb, api_url=api_url, req_args=req_args),
             loop=self._event_loop,
diff --git a/tests/web/test_web_client_coverage.py b/tests/web/test_web_client_coverage.py
index 3802dfbb0..366cc65c6 100644
--- a/tests/web/test_web_client_coverage.py
+++ b/tests/web/test_web_client_coverage.py
@@ -1,4 +1,5 @@
 # Standard Imports
+import os
 import unittest
 
 # ThirdParty Imports
@@ -17,6 +18,7 @@ class TestWebClientCoverage(unittest.TestCase):
     )
 
     api_methods_to_call = []
+    os.environ.setdefault("SLACKCLIENT_SKIP_DEPRECATION", "1")
 
     def setUp(self):
         self.loop = asyncio.new_event_loop()