11 Partners Leave Bingham En Masse for Sidley Eleven partners at the law firm Bingham McCutchen who worked in the firm's highly regarded securities-enforcement practice resigned on Monday to join Sidley & Austin. Among those departing Bingham are Susan L. Merrill, the former head of enforcement at the Financial Industry Regulatory Authority, and Neal E. Sullivan, the head of the practice group. The group represents Wall Street banks and accounting firms in a variety of government investigations and regulatory matters. Reached late Monday, Claire Papanastasiou, a spokeswoman for Bingham, confirmed the move, and said that the firm wished the lawyers well. Carter G. Phillips, the co-chairman of Sidley's executive committee, did not immediately return a request for comment. Lateral moves by partners at large corporate law firms have become commonplace, but 11 partners leaving a firm en masse, especially from such a prominent practice, is unusual. The departures are a blow to the Boston-based Bingham, a 1,000-lawyer firm known for its securities-enforcement work, representing financial services firms before a range of government agencies, including the Securities and Exchange Commission and the Commodity Futures Trading Commission. Given the ever-changing regulatory landscape in Washington and on Wall Street, it is an especially lucrative practice area for law firms. Bingham still has about 20 partners its securities-enforcement practice, as well as dozens of others in its securities group. They include Christopher Cox, the former S.E.C. chairman, who practices corporate law out of the firm's office in Costa Mesa, Calif. The firm made a big splash three years ago when it hired Ms. Merrill, the former enforcement chief of Finra, a private entity that regulates Wall Street. Ms. Merrill, who works out of New York, was previously a partner for a decade at Davis Polk & Wardwell. "Susan is a recognized leader in the securities field," Jay S. Zimmerman, chairman at Bingham, said at the time. Her arrival to Bingham exemplifies our investment and commitment to building the strongest securities team and advising clients in the most complex matters, nationally and globally. Also leaving with Ms. Merrill and Mr. Sullivan is Herbert F. Janick III, a former senior member of the enforcement division at the S.E.C. and general counsel of UBS Financial Services. The departures come a few months after another senior partner in Bingham's securities-enforcement practice, Geoffrey F. Aronow, left the firm to become general counsel at the S.E.C. Mr. Aronow and Ms. Merrill had recently handled several of the firm's prominent securities enforcement cases, including the representation of Christine Serwinski, the former chief financial officer of the North American arm of MF Global, the brokerage firm led by Jon Corzine that collapsed in 2011.