The Supreme Court appears set to deal a major blow to public employee unions. The justices heard arguments Monday in a case brought by the right-wing Center for Individual Rights and backed by other anti-union groups. The case involves 10 California teachers who object to a state law requiring them to pay a “fair share service fee” for collective bargaining activities, even if they choose not to join a union. In 1977, the Supreme Court ruled against forcing non-union members to pay for a union’s political activities, but upheld required payments for collective bargaining. The court now appears likely to overturn that precedent, potentially weakening public sector unions nationwide by allowing workers to opt out of paying for union activities that benefit them.