The problem with Beck is that I don't think it requires the union to tell employees they don't have to pay that part of their union dues. And God-forbid the employer would tell them.
During the Clinton administration, the Labor Department actually forbade employers posting information about Beck on company bulletin boards. Presumably the Bush Labor Department has rescinded that order. If I were an employer with unionized employees, I'd send out a mailer to every one of them. I'm guessing that Californistan won't be doing that for the teachers, however.