I worked at the post office in two different cities in the late 1960s and early 1970s. At that time the nationally set wage was good money in some places and not much in others. In Seattle we had competent supervisors and everyone worked hard. In San Francisco my immediate supervisor was often so drunk he seemed to have trouble standing. A lot of the worker-bees took advantage of this. One man simply clocked in and spent the day playing pool, then came back to clock out. This was not because the union protected his right to do this, but because management allowed it.
Interestingly, it was a strike that changed the dynamic. The strike was not sanctioned by the union. I don't even remember where it started, but it spread to many cities. I was a relatively new employee who didn't even belong to the union but it seemed like a good chance to not go to work for a few days.
After that event, the whole organization seemed to shape up, running more like what I'd experienced in Seattle. I was very young with just a high school diploma looking at the organization from the absolute bottom, but with higher wages it seemed like someone took notice and started to manage for real efficiency.