(WISC) MADISON, Wis. -

Federal labor regulators said the state Department of Transportation has paid Gov. Scott Walker's bodyguards more than half-a-million dollars in overdue overtime.

The U.S. Department of Labor said in a statement Wednesday that its investigators determined the DOT owed nine members of the Dignitary Protection Unit, which provides security for Walker, $577,189 in overtime earned between May 2013 and May 2015. The unit is made up of state troopers. Their pay comes out of DOT's budget because the State Patrol is an agency division.

A DOT spokeswoman said the agency made the payment in November and has changed its payroll system to comply with federal regulations.