That is what strikes are by definition, yes. It doesn't just seem like it. There is no other weapon workers can wield if they don't have a legal basis to make leadership meet their demands.
Obviously this can backfire in countries that don't have good union law and if you are too replaceable (hello AI).
This isn't Extortion because there's no gun to your head saying you HAVE to provide labor. At least in most industries. If I choose not to help you, I'm not extorting anything - you're free to find someone else. If you can't, and I'm your only option, that's still your problem, not mine.
Obviously this can backfire in countries that don't have good union law and if you are too replaceable (hello AI).