UW Madison teaching assistants were represented by a union [1,2] between 1970 and 2011, when its status was abruptly terminated by conservative political forces in Wisconsin. When the union was active, it was pretty clear that negotiating was not its strength, but the union was always available to help people navigate day-to-day problems that come up. Maybe it is just coincidence, but multiple independent accounts detailing toxic work environments within UW have been reported in recent years.
[2] https://en.wikipedia.org/wiki/Teaching_Assistants_Associatio...