An NYPD logo is pictured on wall above makeshift memorial at the site where two police officers were shot in the head in the Brooklyn borough of New York, December 22, 2014.
An NYPD logo is pictured on wall above makeshift memorial at the site where two police officers were shot in the head in the Brooklyn borough of New York, December 22, 2014. Reuters / Carlo Allegri

The former head of one of New York City's police unions was expected to appear in federal court on Wednesday, a source close to the situation said, nearly five months after his resignation in the wake of a federal probe into the labor organization.

Ed Mullins, who was first elected president of the Sergeants Benevolent Association (SBA) in 2002, was not in custody early on Wednesday afternoon, though his status could change as the day progresses, the source told Reuters.

The hearing is expected to be held at the U.S. District Court for the Southern District of New York in Manhattan. NBC 4 New York, citing "multiple police sources," reported that prosecutors were ready to file federal charges against Mullins. The specific charges and timing were not immediately clear.

Mullins, who was a vocal critic of former Mayor Bill de Blasio, was arrested on Wednesday morning, local media reported, citing the FBI. Reuters could not immediately reach the law enforcement agency for comment.

The union declined to comment on the matter. It represents 12,000 current and retired members of the largest U.S. police force, according to its Facebook profile.

The U.S. Attorney's office did not return a call seeking more information.

A federal corruption investigation, which included a raid on the SBA headquarters in Manhattan and Mullins' Long Island residence, led the union's board to ask for his resignation last October. After the raid, Mullins also resigned from his NYPD job, which he held at the same time as the union position.

His resignation was applauded by de Blasio, who was often at odds with Mullins, who frequently used the union's Twitter account to air grievances with the mayor and his administration. Mullins frequently accused de Blasio of being soft on crime and turning his back on the NYPD.

"Ed Mullins dishonored his uniform, his city and his union more times than I can count," de Blasio said in a tweet after Mullins resigned. "It was just a matter of time before his endless hatred would catch up with him."