BOSTON — The former head of the Boston FBI office is expected to plead guilty to an ethics charge in a deal that includes a recommendation from prosecutors that he pay a $15,000 fine, but serve no prison time.

Kenneth Kaiser is due in federal court Thursday for a change-of-plea hearing. The 57-year-old Kaiser was charged with violating a federal ethics law by having professional contact with former FBI colleagues within a year of leaving government service.

Kaiser was the special agent in charge of the Boston office from 2003 to 2006, when he left to become an assistance director at FBI headquarters.

Prosecutors alleged that within a year of retiring from the FBI and going to work for a private company, Kaiser had contact with FBI agents investigating the company.