American Airlines and JetBlue must unwind a partnership that lets them cooperate on flights throughout the Northeastern U.S. after a federal judge in Boston ruled in favor of the Justice Department, which argued that the pairing would lower competition and raise fares.

It’s a much-needed win for federal antitrust prosecutors, who have lost three out of five merger trials under the leadership of Assistant Attorney General Jonathan Kanter, who has helped spearhead the Biden administration’s aggressive stance against anticompetitive mergers and other business practices.