A $69 billion merger between CVS Health and Aetna that promises to transform the healthcare industry may be in trouble after a federal judge raised concerns Monday over the transaction’s anti-competitive effects.

U.S. District Judge Richard Leon, who previously ruled against the government’s challenge to the AT&T-Time Warner merger, warned that CVS may need to keep Aetna’s assets separate as he reviews the deal, according to the Wall Street Journal. That would be problematic since the two firms have already started integrating their operations.