Mayor Michael Bloomberg is suing to try to block a law that would make it easier to sue the NYPD over stop and frisks or other actions people claimed were discriminatory.
The mayor followed through Tuesday on his pledge to go to court over the measure, which the City Council passed last month over his veto.
The suit says the legislation treads into an area governed by state law.
Council Speaker Christine Quinn says she's confident the measure will prevail in court.
The legislation is part of a pair of laws imposing new checks on the NYPD amid complaints about stop and frisk and other tactics. The other creates a police inspector general.
Bloomberg vetoed both. His suit concerns only the police-lawsuit measure.