A federal judge in California Monday blocked a controversial approach to bringing securities fraud suits that began when two firms lost out on their bids to become lead counsel in stock-drop suits targeting McKesson HBOC Inc.

San Jose-based U.S. District Judge Ronald Whyte ruled that Chicago’s Much Shelist Freed Denenberg Ament & Rubenstein must end the practice of soliciting potential plaintiffs in the class action by asking them, through a form letter, to opt out. San Diego’s Milberg Weiss Bershad Hynes & Lerach initially joined in the solicitations but later backed off.