The Newark Star-Ledger reported that the union president, Officer Maurice Gattison, raps under the name "Gat the Great."
He has appeared in numerous videos. One features Gattison rapping about drinking, using an anti-gay epithet and calling himself a "felon for life." In one scene Gattison, clad in a fur coat, sits in a car and tells others they might have to meet a Smith & Wesson. He then briefly points his finger at the camera as though he's firing a gun.
The case has sparked a debate over free speech and whether officers are bound by the same rules of behavior on and off-duty.
"The Irvington Police Department has standards of conduct that apply to on-duty and off-duty behavior," Police Director Joseph Santiago told the paper. He has until next month to file charges against the officers.
Irvington Township Attorney Marvin Braker said the videos were disturbing but could be protected under the First Amendment.
In an interview with the paper, Gattison said he has been rapping for years.
"I could see if I was targeting somebody, but it's just a lyrical exercise," he told the paper.
Gattison said he was asked to perform at the department's holiday party.