(Bloomberg) -- Anthem Inc. and Cigna Corp., the healthinsurers fighting a U.S. antitrust lawsuit, have accused oneanother of breaching their $48 billion merger agreement, theJustice Department said in a court filing.

Related: DOJ says it's open to settlement offer inAnthem-Cigna case

A lawyer for Cigna said during a teleconference last month thatin-house attorneys for the companies had exchanged letters allegingeach violated the deal’s terms, the government said in the filingWednesday in Washington. The Justice Department raised the issue aspart of a dispute over evidence in its lawsuit against the insurersseeking to stop their merger.

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"Governance disputes between defendants have escalated, and thefirms are now accusing each other of breaching the mergeragreement," the U.S. said. "Because the breach letters reveal thecurrent state of hostility between defendants, the letters evincebarriers to integrating these firms and are relevant" to one of thedefenses raised by the companies.

At stake -- in addition to the $48 billion deal itself -- is the$1.85 billion breakup fee Anthem would owe Cigna if the JusticeDepartment wins a court ruling blocking the merger on antitrustgrounds. Under the terms of the merger, Anthem wouldn’t have to paythe fee if Cigna were found to have committed a "willful breach" ofthe agreement.

Company contentiousness

Tensions between Anthem and Cigna have been evident since beforethe Justice Department sued the companies in July to stop themerger, which it says would reduce competition and reduce choicefor consumers. At a court hearing in August, an Anthem lawyer saidthere is "contentiousness" with Cigna and that Cigna intends towalk away from the deal after an April 30 deadline for closing thedeal rather than extend the timing.

Anthem reiterated that the company is firmly committed todefending the deal and declined to comment. Cigna also declined tocomment.

The bad rapport between the insurers stems from before the dealwas struck, when Cigna rejected Anthem’s initial overtures, in partover a dispute about what role Cigna Chief Executive Officer DavidCordani would have at a combined firm. Anthem and Cigna have alsoheld meetings with investors to discuss their prospects if a dealcan’t be completed.

Anthem shares rose 1.8 percent to $127.97 at 3:06 p.m. in NewYork after earlier climbing as much as 2.3 percent. Cigna rose 0.5percent to $132.25.

November trial

The government lawsuit is scheduled to go to trial on Nov. 21.As part of their case, Justice Department lawyers are seeking alldocuments from the companies related to alleged breaches of themerger agreement. The companies are withholding correspondencebetween their in-house lawyers alleging the breaches, thegovernment said in Wednesday’s filing.

The Justice Department says the letters should be producedbecause they are relevant to one of the defenses raised by thecompanies, namely that the merger will create a more efficientcompany and result in billions of dollars in cost savings. Thatrequires cooperation, the government said.

The Justice Department disputes the efficiency claim "in partbecause hostility between defendants could hamper integrationefforts," it said.

The case is U.S. v. Anthem Inc., 16-cv-1493, U.S. District Courtfor the District of Columbia (Washington)

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