Earlier quoted context omitted.
You have the choice to vote. The union voted to strike. Not everyone voted for it, but enough did to initiate the strike. It's usually a fairly unanimous thing. Source: once upon a time, long, long ago, I was on the executive board of a union that may or may not have voted to strike.
But if the vote to strike is going to pass easily, then surely you don't want to be an outcast and vote against it, right? Retaliatory actions from your fellow union members has to be common.
http://www.sfgate.com/bayarea/article/BART-unions-rank-and-f...