diff --git a/src/cad_to_dagmc/core.py b/src/cad_to_dagmc/core.py
index d470060..cb117f7 100644
--- a/src/cad_to_dagmc/core.py
+++ b/src/cad_to_dagmc/core.py
@@ -5,6 +5,7 @@
 from cadquery import importers
 from pymoab import core, types
 import tempfile
+import warnings
 
 
 def _define_moab_core_and_tags() -> tuple[core.Core, dict]:
@@ -347,6 +348,12 @@ def _check_material_tags(material_tags, iterable_solids):
             if not isinstance(material_tag, str):
                 msg = f"material_tags should be an iterable of strings."
                 raise ValueError(msg)
+            if len(material_tag) > 28:
+                msg = (
+                    f"Material tag {material_tag} is too long. DAGMC will truncate this material tag "
+                    f"to 28 characters. The resulting tag in the h5m file will be {material_tag[:28]}"
+                )
+                warnings.warn(msg)
 
 
 def order_material_ids_by_brep_order(original_ids, scrambled_id, material_tags):
diff --git a/tests/test_python_api.py b/tests/test_python_api.py
index b29e9f2..76bbe78 100644
--- a/tests/test_python_api.py
+++ b/tests/test_python_api.py
@@ -3,7 +3,8 @@
 import pytest
 import cadquery as cq
 from cad_to_dagmc import CadToDagmc
-
+import warnings
+from cad_to_dagmc.core import _check_material_tags
 
 from pathlib import Path
 
@@ -208,3 +209,13 @@ def test_export_gmsh_mesh_file_handel_paths_folders_strings(filename):
     assert Path(filename).is_file()
 
     os.system(f"rm -rf {filename}")
+
+
+def test_check_material_tags_too_long():
+    with warnings.catch_warnings(record=True) as w:
+        warnings.simplefilter("always")
+        _check_material_tags(["a" * 29], [1])
+        assert len(w) == 1
+        assert issubclass(w[-1].category, UserWarning)
+        assert "Material tag" in str(w[-1].message)
+        assert "a" * 29 in str(w[-1].message)