The long-running feud between Carl Icahn and Wachtell, Lipton, Rosen & Katz is heading to a new battleground.

In a suit filed Thursday in federal court in Kansas City, Kan., CVR Energy, which Icahn now controls, accuses Wachtell and corporate partners Andrew Brownstein and Benjamin Roth of malpractice in connection with its representation of the oil refining company last year as it attempted to fend off the activist investor’s hostile takeover bid.