Anthem Inc. and Cigna Corp. must disclose to federal antitrust enforcers letters from in-house lawyers in which the insurance companies accuse each other of breaking their $54 billion merger deal, a Washington judge ruled.

The judge, Amy Berman Jackson, agreed with the findings of the retired judge who’s overseeing discovery disputes in the government’s blockbuster antitrust suit, filed in July. Lawyers for Anthem, which is based in Indianapolis, and Cigna, which is based in Bloomfield, Connecticut, had resisted revealing those in-house letters to the U.S. Justice Department.

Government lawyers had argued that the in-house letters would “reveal the current state of hostility between defendants” and illuminate challenges the companies face as they defend their proposed merger. Attorneys for the insurance giants told Richard Levie, the retired judge, that “any disagreements between the in-house lawyers are irrelevant to the efficiencies that can be achieved from the proposed acquisition.”