My sister thought this was ridiculous, how was she supposed to setup her classroom and answer questions afterwards? Unfortunately her boss warned her that coming early and staying late was not allowed.
Once unions start adding work rules like this you'll see a push to disable after-hours emails, banning weekend work, etc. So while the trope of the lazy union worker is deeply flawed, there are some problems for workers who want to go above and beyond (and while most non-tech workers don't get extra compensation for unpaid overtime, tech workers who go above and beyond actually are rewarded with equity)
So the school was expecting teachers to come in early to setup, not paying them for those hours and punishing those that didn't. This isn't a problem created by labor unions, it is a problem created by exploitative companies. And when the company decided how they would address the issue they decided that pre-class preparation wasn't worth paying for.
Or perhaps different people prioritize different things and who are you to judge or say otherwise?
I personally found this as a first step toward a perception shift about tech from which we can all benefit.
Unions for instance can help fight this constant non extra paid "after-hours" working culture that force you to do all-nighters and all this kind of crazy shits just because the industry is seen as a bunch of nerds that are that passionate about programming that stay long hours just for the sake of love/passion for the job itself.