By decision of the USSC, the Union has to represent everyone who works under the Contract(s), whether or not they're a scab.
If you get fired from the Post Office, chances are better than even you'll get your job back, unless you were fired for a felony. Management is so competent in the USPS that regardless of how many times they lose a removal case they keep screwing up the same issues.
Management is the party who makes life in the Post Office so much fun. They are largely people who couldn't hack it in craft for one reason or another, and were promoted to a supervisory position where they couldn't do much damage. Unfortunately, they Post Office also promotes from within soo...........
There is a major call from NAPS (National Association of Postal Supervisors) for the USPS to do something about the little tyrants who are in charge, but change is hard to come by, because they'd have to remove their fellow executives. Instead of firing them, they just get moved from place to place until they retire.