The US Supreme Court today held that a collective-bargaining agreement that clearly and unmistakably requires union members to arbitrate ADEA claims is enforceable as a matter of federal law. The Court did not overrule Gardner-Denver; rather, it distinguished it. The decision was 5-4 with Thomas writing the majority opinion. Here is the cite: http://www.supremecourtus.gov/opinions/08pdf/07-581.pdf
I will blog more about this case after I read it more carefully.