system
Given the following post, respond as if you're commenting on Reddit:
human
Why are libertarians opposed to organized labor?

Is this a misconception? To me it seems that libertarians would be opposed to government involvement in organized labor, for instance, a law forcing individuals to join a labor union in order to join the work force. But if the market determines these sorts of things then why does a libertarian oppose organized labor. If prison guards in Ohio join a union in order to raise their wages I don't see how that isn't the market determining wages. If prison guards refuse to work for anything less than a certain amount and their unity on the issue makes it so that they have to be payed that amount or else they will strike then isn't that just reinforcing the market value of a prison guard? Or, if the price the prison guards ask for is too high, then a new crop of unemployed people that were willing to work for less would presumably take their place. I don't see how this is violating liberty. There's something here I'm misunderstanding, but I don't know what it is.
gpt
Libertarians don't oppose them, they just oppose all of the government protections they have.

Every individual employee, according to libertarians, has the right to quit working (unless you signed some sort of contract that says I'll work for <x> years no matter what). If they all have that right, then surely they can all exercise that right at the same time, if they so choose. If employers find it's problematic to have all of their work force walk out at the same time, well, they'd better start dealing with the union.

That's fine by libertarians. What they don't like is when you have laws that force people to join unions if they don't want to. They don't like that unions have a tendency to physically prevent replacement workers form entering their workplace, meaning that employers don't get the option to replace the people they've fired. 
Unions occasionally get away with beating up 'scabs' which is obviously wrong. Libertarians don't like how difficult it can be to fire someone in a union, etc. Basically, so many contemporary union powers are granted by government legislation, rather than stemming from their inherent value as workers.

There aren't any modern unions that *only* exercise their right to quit, which is the only bargaining chip libertarians think it's ethical for unions to use.