diff --git a/tuf/api/metadata.py b/tuf/api/metadata.py
index 12d294c9f3..49e6db4b28 100644
--- a/tuf/api/metadata.py
+++ b/tuf/api/metadata.py
@@ -37,6 +37,10 @@
 # and currently, we are above 1000 lines by a small margin.
 # pylint: disable=C0302
 
+# We aim to support SPECIFICATION_VERSION and require the input metadata
+# files to have the same major version (the first number) as ours.
+SPECIFICATION_VERSION = ["1", "0", "19"]
+
 
 class Metadata:
     """A container for signed TUF metadata.
@@ -290,6 +294,16 @@ def __init__(
         expires: datetime,
         unrecognized_fields: Optional[Mapping[str, Any]] = None,
     ) -> None:
+        spec_list = spec_version.split(".")
+        if (
+            len(spec_list) != 3
+            or not all(el.isdigit() for el in spec_list)
+            or spec_list[0] != SPECIFICATION_VERSION[0]
+        ):
+            raise ValueError(
+                f"Unsupported spec_version, got {spec_list}, "
+                f"supported {'.'.join(SPECIFICATION_VERSION)}"
+            )
         self.spec_version = spec_version
         self.expires = expires