A federal judge in Washington has blocked another giant health care merger: insurer Aetna had been hoping to buy Humana for some $37 billion. Judge John Bates found the merger would violate antitrust laws, and also sided with the government on a dicey issue involving the Affordable Care Act.

When Aetna pulled out of the Obamacare exchanges in 11 out of 15 states last summer, it said it did so purely for reasons of profitability. Documents that have come out in this case suggest Aetna was using its participation in the Obamacare exchanges as a bargaining chip with the U.S. government. Aetna said it may appeal this week’s merger decision.