U.S. Rep. Pete Visclosky, D-Merrillville, confirmed Monday he has hired a nationwide law firm in the wake of a federal probe into a Washington lobbying group that has been his top campaign contributor.

The congressman said he is seeking advice from Perkins Coie, one of the pre-eminent firms in campaign finance law, for help in complying with Federal Election Commission rules in the future.

The firm's hiring comes four months after the FBI raided the offices of The PMA Group, of Arlington, Va., a firm that has been Visclosky's biggest single source of campaign cash since 2003. It has funneled $179,450 to him in the last eight years, federal records show.

The New York Times reported Saturday that federal investigators appear to be examining PMA's relationship with Visclosky and are questioning people about the congressman and his staff.

The U.S. Attorney's office in Hammond declined comment on any federal investigation Monday. A spokesman for the FBI office in Indianapolis couldn't be reached for comment.

Jacob Ritvo, a spokesman for Visclosky, said Monday, "Neither Congressman Visclosky nor any members of his staff have heard from law enforcement officials of any kind regarding this case. Any suggestion that he is a subject of the investigation is based entirely on speculation."

Ritvo said Visclosky has voluntarily reviewed his campaign finance reports and found only minor errors that have since been corrected. The congressman said earlier he is returning $16,000 from two donors linked to the beleaguered PMA firm.

Ritvo said Visclosky "sought legal counsel from a top FEC compliance law firm to ensure his FEC filings adhere to the letter of the law."