The union of graduate teaching assistants at the University of Wisconsin seems to be collapsing. Essentially, it won't be able to raise enough cash without automatic deductions from paychecks. It's notable in particular because it is the grand-daddy of all such student unions.
There was a strong unionization effort at the University of Minnesota when I was a graduate student there. I was not a supporter. Indeed, I thought the deal that Minnesota gave me was great, and I felt more grateful than exploited. In return for about 10 hours per week of work as at teaching assistant, I got all my tuition paid for, plus plenty of money to live on. I had a nice apartment, a car, food money, and beer money. In addition, I had pretty good health care coverage. What more could a graduate student ask?
The fact is that the science and math departments have money to support their graduate students. This is because of the research money that flows in and the huge introductory undergraduate classes that bring in tuition money. The humanities are much more cash-strapped, and the pay and benefits to graduate students in those departments was not as good. Much of the debate during the unionization effort was between the two groups of students, with humanities graduate students and union leaders advocating for "equality" in these wages across departments. The vote split down these lines, with science and math strongly voting "no" and humanities "yes"... the union movement failed.
Really, if you want to get a PhD in French poetry, best of luck to you. But don't expect me to chip in to fund your folly.