KBB, a strike vote is usually done well ahead of an actual release to strike. It needs to be done per the union bylaws before a strike can happen, so checking that box off early is smart so you aren't rushing to get it done during a cooling off period. It also does send a good loud message to management, and it lets the NMB know that the pilot group is behind the union, which is something that they need to know before allowing a strike. The NMB's worst nightmare is allowing a strike and then coming to find out that the company gets 25% of the pilots to cross the line and keeps operating in a state of limbo for months on end, bringing tons of bad press and pressure on the NMB. By seeing that everyone is unified, it lets the NMB know that a release will probably result in a deal rather than a strike, and that's what they want.