They also negotiated to discontine coverage for various women's health issues.
Just before COVID, UC Santa Cruz went on a wildcat strike because the union negotiated pay for that campus below the cost of living. A bunch of foreign students lost their visas as a result.
In the second two cases, the grad students tried, but failed to organize against the union.
Most obvious routes to correcting the situation are illegal. In particular, organizing a strike against the union, or organizing a replacement union would have been illegal.