The FBI raided the Manhattan headquarters of the NYC Sergeants Benevolent Association and the Long Island home of its controversial president on Tuesday, in connection with a criminal probe being overseen by federal prosecutors in Manhattan.

The FBI confirmed the bureau executed the search warrant at the police union's offices, as well as a home in Port Washington. A source familiar with the investigation said it was the home of longtime union boss Ed Mullins.

Sources say the warrants were tied to a criminal investigation being overseen by prosecutors in the Southern District of New York. It was not immediately clear, however, who or what they were investigating.

The SBA represents 13,000 current and former members of the NYPD, according to its website; it describes itself as the fifth-largest police union in America. An attorney for the union did not immediately return a call for comment.

Mullins is a controversial figure who has publicly sparred with Mayor Bill de Blasio and with NYPD leadership. De Blasio on Tuesday confirmed the raid at the SBA's office but said he did not have details.

Last month Mullins faced an NYPD internal trial on a variety of administrative charges, including for an episode where he tweeted an arrest record for the mayor's daughter.