diff --git a/conan/cli/cli.py b/conan/cli/cli.py
index bd6c15a24ca..1e10b08358c 100644
--- a/conan/cli/cli.py
+++ b/conan/cli/cli.py
@@ -18,6 +18,7 @@
 from conan.internal.cache.home_paths import HomePaths
 from conan import __version__
 from conan.errors import ConanException, ConanInvalidConfiguration, ConanMigrationError
+from conans.util.files import load
 
 _CONAN_INTERNAL_CUSTOM_COMMANDS_PATH = "_CONAN_INTERNAL_CUSTOM_COMMANDS_PATH"
 
@@ -37,6 +38,29 @@ def __init__(self, conan_api):
         self._groups = defaultdict(list)
         self._commands = {}
 
+    @staticmethod
+    def _warning_custom_commands_imports(custom_commands_path):
+        # Protect against usage of internal API
+        forbidden = ["from conan.internal", "from conan.tools", "from conan.test", "from conans"]
+        fails = {}
+        for root, _, fs in os.walk(custom_commands_path):
+            pyfiles = [os.path.join(root, f) for f in fs if f.endswith(".py")]
+            for f in pyfiles:
+                text = load(f)
+                for forbid in forbidden:
+                    if forbid in text:
+                        fails.setdefault(forbid, []).append(f)
+        if fails:
+            ConanOutput().warning("*" * 80)
+            for forbid, files in fails.items():
+                ConanOutput().warning(f"Forbidden internal import'{forbid}' in:")
+                for f in files:
+                    ConanOutput().warning(f"    {f}")
+            ConanOutput().warning("")
+            ConanOutput().warning("These imports will change in future releases")
+            ConanOutput().warning("Please, use only public documented API in docs.conan.io")
+            ConanOutput().warning("*" * 80)
+
     def add_commands(self):
         if Cli._builtin_commands is None:
             conan_cmd_path = os.path.join(os.path.dirname(os.path.abspath(__file__)), "commands")
@@ -61,6 +85,8 @@ def add_commands(self):
             if not os.path.isdir(custom_commands_path):
                 return
 
+            self._warning_custom_commands_imports(custom_commands_path)
+
             sys.path.append(custom_commands_path)
             for module in pkgutil.iter_modules([custom_commands_path]):
                 module_name = module[1]
diff --git a/test/integration/command_v2/custom_commands_test.py b/test/integration/command_v2/custom_commands_test.py
index cea9c844b00..2449c55934e 100644
--- a/test/integration/command_v2/custom_commands_test.py
+++ b/test/integration/command_v2/custom_commands_test.py
@@ -469,3 +469,26 @@ def mycache(conan_api, parser, *args, **kwargs):
         c.run("mycache")
         # Does not break unexpectedly, caching is working
         assert "WARN: Cache invalidated, as expected: Invalid URL 'broken" in c.out
+
+
+class TestCustomCommandsImports:
+
+    def test_import_warning(self):
+        mycommand = textwrap.dedent("""
+            from conan.cli.command import conan_command
+            from conan.internal.paths import DATA_YML
+            from conans.util.files import load
+            from conan.api.output import ConanOutput
+
+            @conan_command()
+            def mycache(conan_api, parser, *args, **kwargs):
+                \""" this is a command with subcommands \"""
+                ConanOutput().info(f"DATA_YML: {DATA_YML}")
+            """)
+
+        c = TestClient()
+        c.save_home({"extensions/commands/cmd_mycache.py": mycommand})
+        c.run("mycache")
+        assert "WARN: Forbidden internal import'from conan.internal' in:" in c.out
+        assert "WARN: Forbidden internal import'from conans' in:" in c.out
+        assert "DATA_YML: conandata.yml"