TRENTON, N.J. — Gov. Chris Christie announced the resignation Friday of one of his top appointees amid an escalating probe into whether Christie loyalists deliberately created traffic jams at a bridge into New York City in an act of political retribution. The governor denied the lane closings were politically motivated.

The resignation of Port Authority of New York and New Jersey deputy executive director Bill Baroni comes a day after a state lawmaker issued seven subpoenas to Baroni and other agency officials and the Democratic National Committee tried to link the controversy to Christie, a potential 2016 Republican presidential candidate.

Christie painted Baroni’s departure from a plum appointment as an expected move.

The issue involves the George Washington Bridge. The town on the New Jersey side of the bridge is Fort Lee, whose Democratic mayor did not endorse Christie in last month’s election.

On Sept. 9, two local-access lanes from Fort Lee to the bridge were closed without warning. Officials at the Port Authority, which operates the bridge, said the closures were for a traffic study. The closures led to gridlock in Fort Lee.