I'm a bit confused by the question, which could be the reason we haven't seen a good answer.

It sounds like you're saying that the cockpit crew (Pilot, CoPilot etc) don't have a choice regarding flying past a certain limit. They're forbidden not by (or not only by) their contract, but FAA regulations.

But FAs may be a different matter, so the question is whether there are regulations that limit how much an FA can be on his/her feet? Some limit that cannot be waived by the employee?

There's really no reason to get into the wisdom of work rules written into a contract; as I read it, that's not the question. The only question, if I'm reading this right, is whether FAs have work rules that are FAA requirements (and thus not able to be waived).

So... do FAs have absolute work limits that are FAA imposed?

Thanks-