Forgive my naivete but what can the unions really do if AMR simply honors the concessions as of May 1st that the union members voted for?

So the unions file legal motions to block the concessions. Everybody spends a **** load on lawyers so that a judge decides to rule in their favor 6 months later at which time AMR files bankruptcy and the courts require even stiffer concessions.

I'm having trouble understanding what the unions think their leverage is. Blustering FAs are not a strength.