Six city lawmakers are suing to block the Big Apple’s embattled Board of Elections from rolling out a new ranked-choice voting system next year, claiming officials have failed to prepare for the potentially confusing switchover.

The lawsuit is the latest salvo lobbed by mainstays of the Brooklyn Democratic Party against the new elections system, which will do away with the runoff elections that Gotham’s political machines have dominated for decades.

In the court papers filed late Tuesday, the half-dozen lawmakers and a slew of civil rights groups argue that BOE failed to provide a required report due in June showing it has prepared for the switchover and also failed to launch the required advertising campaign to educate voters about rank-choice voting.

They also claim that the federal Voting Rights Act should be invoked to prevent the changes but do not outline how rank-choice voting violates the landmark civil rights-era law.