Earlier quoted context omitted.
What do you mean by "extort", exactly? Refusing to perform work for a pay that is too low is pretty much the essence of free market. Why are you okay when individuals do it separately, but suddenly not okay when they band together?
They band together and then they be like: we want 50% wage increase or we all quit and you lose a lot of money in the process. This is what I mean by extort.
The only reason to be offended by it specifically when people do it collectively rather than individually is because in the former case they actually have enough bargaining power vs their employer to get a better price for their labor. That is, because the market is "too free" to produce the desired (low) price of labor.