Should Christians ever join a labor strike?
I think the question arises because there are several allegiances involved. And you have biblical teaching to the effect that having humility, showing submission, and being wronged are good ways to bear witness to Christ. So I want to say that I don't think Christians are eager to use coercion to get their way in their employment.
I don't think it would be typical of the spirit of Christ for a band of employees to get together and say, "Now if we all do this, we'll corner our employer and he'll have to do this." That's just not the spirit of the way Christians go about enacting change.
Now having said that, I'm putting some resistance on coming easily to the conviction that one should use a coercive tactic like a strike in order to get some benefit.
Nevertheless, I want to also say that employers, historically, have proved at times to be very unjust. And Christians care about injustice. They care about the single mom who is trying to put bread on the table, or the dad who has three kids at home, a wife who can't work, and who is being ripped off by this employer because of the meager wage he is being paid. Unions rose up to address those kinds of injustices, and they got the clout to do it by combining a lot of weak little people into one stronger phalanx.
And so I think a Christian would say, "Let's use our union as much as we can to be helpful to employers, to show them what would be right and good." But if the time comes when a genuine injustice is being answered by a group strike, then the Christian has to make the call as to whether this is the moment when justice demands that kind of witness, or whether there is way too much ego, pride, and greed driving the union and he shouldn't be a part of it.
So that's an answer that allows for participation, I think, but would discourage it and would seek other ways forward in relationships between management and labor.