Since you've piqued my interest Colonel, I've done a little research, having held a grudge for decades as the Musician's union shut me down while playing a gig, presumably because I, just out of the Army, didn't yet have a union card. They threatened my colleagues, all of whom had cards. They assured me it was because it was a mixed group, and the union didn't approve of blacks playing certain kinds of gigs (I was the only white). The Unions all but shut down live music in the major West Coast City I called home.
The two postal workers unions, postal workers and letter carriers are both AFL/CIO, same core union as SEIU. Are suggesting that they don't play as dirty as the SEIU, that hired Acorn to train their cadres? Would postal workers lose overseas ballots? While counts cannot be verified, having unions handle presumed votes before they are tabulated is, as I suggested before, just one of the reasons our voting systems cannot be presumed to represent the will of voters.
Not many postal workers would tamper with the mail due both to a sense of duty and fear of consequences, but I suppose it would only take one.