Federal prosecutors have widened the scope of their investigation into the workings of the Port Authority of New York and New Jersey and are now looking into whether the administration of Republican New Jersey Gov. Chris Christie retaliated against Democratic Jersey City Mayor Steven Fulop after Fulop declined to endorse Christie for re-election in 2013.

The U.S. Attorney’s Office for the District of New Jersey served the Port Authority with a subpoena this past week demanding records that document relations between the bistate agency and Jersey City. The issuance of the subpoena was first reported by the Wall Street Journal on March 19.