New York City’s police watchdog is probing allegations by the NYPD’s biggest union that its investigators are anti-cop radicals, The Post has learned. 

The Police Benevolent Association  (PBA) in a May 7 letter demanded the firing of a Civilian Complaint Review Board supervisor and seven investigators, citing social media posts and college essays by the investigators the union called “blatant examples of anti-police bias.”

Some of the board’s employees posted “A.C.A.B.” — an anti-police acronym for “All Cops Are Bastards” on social media, and others wrote posts and essays about the elimination of police, the PBA found.

“The agency has begun an internal review of the PBA’s allegations,” CCRB Executive Director Jonathan Darche recently wrote to a group of city councilmembers demanding an investigation.

“The allegations concerning varying social media posts require careful review to determine the appropriate action, if any, to be taken with consideration, as well, of employee protections,” he added.

The CCRB initially responded to the PBA that its investigators review cases fairly and impartially. 

It changed its tune after the eight councilmembers fired off a May 28 letter raising “serious questions about the fairness of CCRB investigations and the reliability of substantiated findings in which the employees played a role.”

Councilmembers Phil Wong, D-Queens, Kamillah Hanks, D-Staten Island, Vickie Paladino, R-Queens, Darlene Mealy, D-Brooklyn, David Carr, R-Staten Island, Inna Vernikov, R-Brooklyn, Joann Ariola, R-Queens and Frank Morano, R-Staten Island, also called for the employees to be placed on administrative leave pending the outcome of the probe. 

CCRB investigators look into civilian reports of misconduct by NYPD officers. The cases, which are not criminal, can lead to internal charges and punishment.