A past post from Doug Wilson's blog that I thought worth repeating:
Just a quick note about "collective bargaining." The real question for those who would understand the nature of unions is the question of ownership. Say there is a particular job at the office building, or at the factory, or in the shop on Main Street. Who owns that job?
The assumption behind collective bargaining is that the one who holds the job owns the job. The biblical understanding is that the one who offers the job owns the job (Matt. 20:15). This is not the same as saying that the employer is a great guy. No, the owners of jobs are frequently evil, and they abuse their position of ownership (Jas. 5:4).
Labor/management disputes often fall into a false good guy/bad guy dichotomy, and it betrays a false understanding of the antithesis. In the Bible the owners are often the bad guys. But that does not mean they are not the owners of the jobs they offer. Bad guys can own things. And the commandment does not say, "Thou shalt not steal, except from bad guys."
So there is absolutely nothing wrong with employees collectively deciding that conditions on the job are horrendous, and deciding en masse that they don't want to work there anymore. And there is no problem with them negotiating with the owner from that collective position. Say they are asking for a raise, or for safer working conditions. That is fully legitimate as well. What is not legitimate is for them to lock up the job they have abandoned as though they are the owners of it. To refuse to work a job that you simultaneously lay claim to is a claim of ownership, which in this case is a false claim.
This sin (and it is a sin) is in evidence when strikers attack what they call "scabs." Scabs are workers looking for employment, and the horrendous conditions on the abandoned job would, in their instance, be an improvement.
In other words, collective bargaining is nothing but extortion, and Christians should do everything in their power to have nothing to do with it.