I think the issue is that there was full transparency on pay (a fixed base rate plus a fixed percentage) and then it was changed without warning.

I work for a salary, which is fully transparent in the sense that I know what my next paycheck will be to the penny. (It’s not transparent in how it’s set, but it is week-to-week.) If my employer started paying me based on effort, and didn’t tell me what constituted effort, not only would I be pissed off but that would be completely illegal.

I’m not suggesting that this change is or should be illegal. But if it happened to me I’d find it extremely unfair.