In order to prove that libertarians are hostile to unions in general, and not merely hostile to them receiving special favors or benefits from the government, a staunch progressive referenced an article by Professor William Hutt: Trade Unions: The Private Use of Coercive Power. In it, Professor Hutt makes the argument that the strike or threat of a strike is a coercive act.
That article is actually little better than a diatribe against the economic ignorance of unions, their members, and their leadership. While it is clear that Professor Hutt stops short of forbidding unions the right to act, and thus the article does fit in within the realm of libertarian thought, it is also clear that the article is quite far off base when it describes a strike as coercion.
Only at the very end of the article does Professor Hutt actually get to one of the legitimate critique of unions expressed by libertarians, and that is their political activities to get them special favors or special benefits from the government.
But by calling a strike "coercion" he opens the door for asking for government intervention, the step he stops short of. If there must be a government, acting against coercion, acting against the use of force or the threat of force, is one of the few areas where it should act.
If there is a right to conduct business, there is also a right to not conduct business. It cannot be coercion to refuse to conduct business. There cannot be one without the other. That is what a strike is. And unions themselves are a right of free association.
The other factor is that he describes how unions hurt their own cause. Take any issue libertarians stand for, and it is obvious that libertarians have absolutely no interest in stopping people from hurting themselves. This is evident in every single moral issue on which libertarians and conservatives disagree.
The only redeeming factor in the essay is that Professor Hutt did stop short of advocating legal restrictions on unions. But he is truly straying beyond libertarian thought when he goes so far as to call striking or threatening to strike by the term "coercion."