Rob Weir on why libertarians oppose labor unions

If unions were truly voluntary, with respect to all parties, I don’t think there would be any principled opposition to them from a libertarian. However, depending on time and place, labor unions have historically fallen far short of this ideal:

• Early labor unions were racist, refusing to represent minority workers, and organized with the specific goal of keeping African Americans and immigrants from getting jobs in industry.
• Labor unions were instigators of violence, both against the persons and property of factory owners, but also against workers who did not sufficiently support a strike, and members of the public who bought products made by the factory while on strike. 
• Labor unions, as they became part of the Democrat political machine, sold their souls in return for monopoly state privileges, including closed shops, agency fees, prevailing wage laws, etc.

Although labor unions have lost much of the power they once held in America, they still operate by a state-granted monopoly. Once a work site has unionized, individual workers at that location have zero choice in the matter. They must go with the selection of the majority. This is not a voluntary solution.

Imagine unionization was voted down, at a particular factory, 60% to 40%. Why should the 40% be denied union representation if they so desired it for themselves?

Similarly, suppose 60% want to be unionized, but 40% want Union A and 20% want Union B? Why should one be granted a monopoly, and forced on the others? A voluntary market approach would have Union A represent the 40% who want them, and Union B represent the 20% who want them, and no representation at all for the 40% who want none.

In other words, selecting an organization to represent your interests to your employer should be as free a choice as selecting a bank, a barber, or a bicycle. Your ability to make a choice according to your preferences should not depend on your preferences being in the majority.

Of course, you can argue that having a single union would be more efficient, with less overlapping effort, etc. But efficiency, to a libertarian, is not an argument for denying freedom. You could just as well argue that it would be “more efficient” to ban many churches where they appear to have relatively minor doctrinal differences, and force them into a single church. That would make just as much sense, and would be just as anti-liberty.

Finally, unions are not voluntary with respect to the employer. It is illegal for an employers to refuse to recognize or negotiate with the union. It is illegal for an employer to fire a worker for striking and replace them with another worker. It is illegal for an employer to give a bonus to non-striking workers unless the same bonus is also given to striking workers.

Although it is not beyond the theoretical possibility that an employer could agree to limitations like the above voluntarily, in practice this has never occurred, at least not to my knowledge. These are restrictions placed on one party, for the sole benefit of the other party, by an government that seeks to benefit politically by granting this privilege. This is far from voluntary, and a libertarian would naturally oppose such coercive actions and abridgments of free association.

~ Rob Weir, Quora answer, October 17, 2019