1. AT&T Mobility LLC v. Concepcion: This case involved a class action lawsuit against AT&T for charging sales tax on phones that were advertised as free. The Supreme Court held that the Federal Arbitration Act (FAA) pre-empted state laws that deemed class-action waivers in arbitration agreements unenforceable. This decision strengthened the enforceability of mandatory arbitration agreements and limited the ability of states to invalidate them.