The ruling stems from the union's failure to file a document with the NLRB at least 30 days before declaring a strike.

"It is very unfortunate that our musicians were persuaded to engage in an unnecessary and illegal strike when this entire situation could have been avoided," Adams said.

The orchestra has not performed since January 3, when the musicians' union turned down a contract offer from management, Musicians have repeatedly called the work stoppage a lockout; management has said it's a strike, a position that has apparently been validated by the NLRB's ruling.

Union lawyer Leonard Leibowitz told the St. Louis Post-Dispatch that he thought it was unlikely that the NLRB's general counsel would authorize court action. And even if the board gets an injunction, he said, "all that happens then is that the musicians would have to go back to work for 60 days" before striking again.

"This will not get a settlement," he added. "This is all fun and games, but it will not get a settlement."

In his statement, Adams said that "the symphony looks forward to getting back to the negotiating table and working together to put this chapter behind us." But Leibowitz told the Post-Dispatch that Adams had rebuffed the efforts of a federal mediator to restart talks.