"When a singer, who works on a freelance basis and whose livelihood is dependent upon Pamela Rosenberg's good will, is 'asked' by her to perform at a birthday party, that singer has no real option," said AGMA executive director Alan Gordon in a statement. "In keeping with its policy of disregarding its contractual obligations, however, the Opera simply refused to ask the union and, instead, pressured its singers into entertaining Runnicles' birthday guests."

The lawsuit contends that SFO ignored union grievances filed over the gala concert, as well as complaints about a long list of other issues, all in violation of the singers' 2003 contract. According to the union, the contract gives the company a limited amount of time in which to resolve grievances or enter arbitration.

Also among the 25 grievances that the SFO allegedly ignored were those over its failure to provide costumes for a gala performance with Ren_e Fleming (choristers were asked to provide their own tuxedos); to give chorus members first consideration for smaller roles; and to compensate the union for not filling two chorus jobs.

AGMA also said it was preparing to file a complaint with the National Labor Relations Board, claiming that the SFO did not bargain in good faith last year, when the union accepted a two-year pay freeze because of the opera's claims of financial distress. According to the union, Runnicles received a pay increase of 40 percent in 2002.

San Francisco Opera told the New York Times that it was reviewing the lawsuit, and would not yet respond to its allegations. But officials told the paper that Runnicles' pay went up because he conducted additional performances. Soprano Carol Vaness, who appeared at the Runnicles gala, said that she had not been pressured to perform. "Every single person at the gala that I know‹and I knew just about everybody‹was there with great respect for Donald Runnicles," she said.