The NYPD can’t harass a group of sergeants who joined a lawsuit against the department claiming they were cheated out of overtime pay, a federal judge ruled.

In 2006, the Internal Affairs Bureau began investigating some of the thousands of current and former sergeants participating in the suit.

The sergeants won a preliminary injunction barring the NYPD from “retaliating . . . and attempting to coerce plaintiffs to alter their sworn deposition testimony.”

Judge Rosemary Pooler said the injunction “continues to be necessary to protect the sergeants so long as the legal proceedings are ongoing.”