An Anthem spokeswoman declined to comment on the Journal report. Cigna officials were not immediately available to comment.
In a series of letters between top officials including their chief executives, the Journal said Anthem and Cigna accuse each other of violating the July merger agreement and fumbling submissions to regulators.
A key point of contention is Anthem's lawsuit against Express Scripts, a middleman for prescription drugs, according to the newspaper. The suit accuses Express Scripts of overcharging Anthem for drugs.
Cigna Chairman Isaiah Harris Jr., in an April 9 letter to Anthem's board, said the suit could hurt the prospects for regulatory approval and the combined company's value, the Journal said. Anthem responded to Cigna's board that it had alerted Cigna to the possibility of a lawsuit early in their merger talks, and that getting better prices from Express Scripts could only be beneficial, the newspaper reported.