Strikes always have been of grey legality, because the law has always been much more responsive to the concerns of business owners and investors than to those of the workers. There are many examples of historical strikes that ended in workers being gunned down by the army.
The bargaining table is always going to be tilted away from the workers, which is how you end up with collective bargaining agreements like this: with clauses that allow workers to be forced to work involuntary overtime and that make workers using their power to renegotiate the agreement illegal.
But that doesn't mean we should accept that fact or call it "reasonable". It's not. It never has been. It never will be.
This is why I don't believe unions are the solution to issues of inequity and abuse in the workplace. They are a bandaid and a poor one at that. The solution is for the people who are doing the work to also be the ones governing the business. And for the people who provided the capital to merely be given a reasonable return, and nothing more.