diff --git a/asdf/_asdf.py b/asdf/_asdf.py
index 4afaedd0f..c9acb4749 100644
--- a/asdf/_asdf.py
+++ b/asdf/_asdf.py
@@ -17,7 +17,6 @@
 from ._helpers import validate_version
 from .config import config_context, get_config
 from .exceptions import (
-    AsdfConversionWarning,
     AsdfDeprecationWarning,
     AsdfManifestURIMismatchWarning,
     AsdfPackageVersionWarning,
@@ -169,10 +168,6 @@ def __init__(
         self._ignore_unrecognized_tag = ignore_unrecognized_tag
         self._ignore_implicit_conversion = ignore_implicit_conversion
 
-        # Set of (string, string) tuples representing tag version mismatches
-        # that we've already warned about for this file.
-        self._warned_tag_pairs = set()
-
         # Context of a call to treeutil.walk_and_modify, needed in the AsdfFile
         # in case walk_and_modify is re-entered by extension code (via
         # custom_tree_to_tagged_tree or tagged_tree_to_custom_tree).
@@ -1592,20 +1587,6 @@ def search(self, key=NotSet, type_=NotSet, value=NotSet, filter_=None):
         result = AsdfSearchResult(["root"], self.tree)
         return result.search(key=key, type_=type_, value=value, filter_=filter_)
 
-    # This function is called from within TypeIndex when deserializing
-    # the tree for this file.  It is kept here so that we can keep
-    # state on the AsdfFile and prevent a flood of warnings for the
-    # same tag.
-    def _warn_tag_mismatch(self, tag, best_tag):
-        if not self._ignore_version_mismatch and (tag, best_tag) not in self._warned_tag_pairs:
-            message = (
-                f"No explicit ExtensionType support provided for tag '{tag}'. "
-                f"The ExtensionType subclass for tag '{best_tag}' will be used instead. "
-                "This fallback behavior will be removed in asdf 3.0."
-            )
-            warnings.warn(message, AsdfConversionWarning)
-            self._warned_tag_pairs.add((tag, best_tag))
-
     # This function is called from within yamlutil methods to create
     # a context when one isn't explicitly passed in.
     def _create_serialization_context(self, operation=_serialization_context.BlockAccess.NONE):