A top U.S. Justice Department lawyer apologized to a federal judge on Monday for allowing his bar license to lapse as his name appeared on filings in a case challenging the Trump administration’s move to subvert state regulations for vehicle emissions.

In a letter, Assistant Attorney General Jeffrey B. Clark said he discovered Dec. 9 that his license to practice law in Washington had been placed on “inactive status” in early October “for inadvertent non-payment of that year’s dues.”