So, it's definitely the case that the FAA preempts state laws banning required arbitration. However, Amex is not about whether a class action arbitration waive

So, it's definitely the case that the FAA preempts state laws banning required arbitration. However, Amex is not about whether a class action arbitration waiver is enforceable in the face of a state law holding them unconscionable. Instead, Amex is about whether a class action arbitration waiver is enforceable in the face of it just being "too expensive" to arbitrate individually. There was no state law at issue. Just a straight policy argument. The answer to that is quite clearly "yes, it's enforceable". But the opinion goes to great pains to say such waivers are a matter of contract law, which is very traditionally the role of the states. Hence my assumption is that if a state did say that, as a matter of contract law, class action arbitration bans are against public policy, it would be a matter of preemption, and i can't see why the state would lose on the law (though they may lose anyway given the current court makeup)