Dec 1 (Reuters) - The U.S. Transportation Department said Monday it may withhold up to $30.4 million in federal highway funding from Minnesota over commercial driver licenses issued improperly to non-U.S. residents.

The letter to Minnesota Governor Tim Walz gave the state 30 days to come into compliance and revoke the licenses after a federal audit. In September, the Transportation Department issued emergency rules to drastically restrict commercial driver licenses to non-U.S. citizens after a fatal crash in Florida and a government audit.

(Reporting by David Shepardson; Editing by Leslie Adler)