An at-large voting system for electing members to the East Ramapo school board — long dominated by Orthodox Jews whose children attend private yeshivas — has prevented public school parents who are largely black and Latino from electing candidates of their choice, according to a lawsuit filed on Thursday by the New York Civil Liberties Union.

“What we have in East Ramapo is a common case of disenfranchisement of minority voters in the extreme,” said Donna Lieberman, executive director of the New York A.C.L.U. “The system allowed for the white community that does not send its children to public school to hijack the school board.”

The complaint, filed along with co-counsel Latham & Watkins in the United States District Court for the Southern District of New York against the school district and the State Department of Education, argues that the election system violates the federal Voting Rights Act by denying “minority citizens an equal opportunity to have a voice in the future of their community’s public schools.”

A “toxic combination of an at-large elections system and racially polarized voting,” the lawyers say, has made it seemingly impossible for candidates backed by minority voters to win “even a single contested election in the past decade.”