A spat between Wachtell, Lipton, Rosen & Katz and billionaire Carl Icahn stemming from Icahn’s hostile acquisition of CVR Energy Inc. took a new turn Tuesday. CVR revealed that it’s under investigation over securities disclosures it made before the takeover—and it blamed Wachtell for putting the company in the SEC’s sights.

In a letter to U.S. District Judge Richard Sullivan in Manhattan, CVR lawyer Herbert Beigel wrote that the U.S. Securities and Exchange Commission is investigating whether CVR properly disclosed the structure of investment banker fees it agreed to prior to Icahn’s successful 2012 takeover bid.