There are about 1800 UCSC graduate students [1]. From this 2014-15 UCSC budget report [2] there is a very near 2:1 masters:phd graduation ratio. Assuming there are 2 years of masters students and 6 of PhD at any one time, that makes PhD students 60% of “graduate students”. Let’s make this easy by saying 1000 PhD students (if anything I imagine it’s way less than this — as I understand, monetizing masters students has…
And this is why unions exist in the first place and make binding contracts - no one wants to make a deal with another party when the other will arbitrarily decide the deal isn't good anymore and act like fools contrary to the terms of the contract.