Under the Railway Labor act, the National Mediation Board will offer binding arbitration as one of the final steps in the bargaining process, but both parties must agree for it to be binding. If just one party declines the NMB will declare the 2nd Impasse and the 30 day cooling off period will start until self help can begin (strike or lockout). In the event of a PEB, the parties are delayed from pursuing self help but may be required to be at the bargaining table by law. The PEB could perform binding arbitration probably only if both parties agree to it. Also with a PEB, congress could impose the terms of a new contract (scary).