When Haynes and Boone hired Harvey Kesner for its fledgling New York office in 2006, the firm welcomed his corporate group as an illustration of its “careful selection” of laterals who shared its “collegial and entrepreneurial spirit.”

Relations between the law firm and Mr. Kesner can hardly be called collegial these days. Dallas-based Haynes and Boone asked Mr. Kesner to leave last year, and last month, the former partner sued the firm in the Southern District of New York for wrongful termination, demanding $15 million in damages.