Many people think most postal workers are Democrats, but after working there a number of years I found many co-workers who were Republicans and not shy about saying so. Overall, it was estimated that about 40% of postal workers are Republicans.
Nevertheless, the leftist propaganda from the unions heads was relentless. In the lunchroom were posted weekly/monthly newsletters from postal union presidents within a three state area.
Many of their messages weren't just liberal, many of them were heavily anti-capitalist i.e. socialist.
There are four different types of non-management postal workers: carriers, rural carriers, clerks, and mail handlers. They all have their own unions.
The carrier union officials at my workplace were loudly anti-Republican although that was supposed to have been prohibited. Some carriers had calendars that listed how many days before Bush II terms were finished. P.O. officials did make them take them down, but the anti-Republican sentiment was still very strong among the carriers.
I worked in a smaller p.o., and I assume the unions in the big cities are a lot more vehemently anti-Republican.