Unfortunately they can't fire them! It is even worse than trying to fire teachers with tenure.
Same as the no layoff clause in their contract so they just find somewhere to stuff them and keep on paying!(Just heard a government spokesman tell that one today)
Actually their day of reckoning is coming! My bro-in-law works at a sorting center scheduled to be closed. He doesn't know if he'll be relocated or laid off. And he's been there better than 25 years. He has been on third shift because as they have cut back due to attrition and layoffs over the years, he is low man in seniority. He has stayed there because he thinks his chances are better there, than to be low man at a local post office.
The local post offices will be cutting back once the Saturday delivery is nixed. I think we can do with 5 day mail delivery.