The unions want job security. Boeing is farming more and more of it’s work out to contractors, and there is no way for the union to make sure those contractors are also union. So that is what they are striking about. The rest of it is most likey just posturing.
If I was Boeing, this is something that would tell me to start farming even more stuff out. This is what has gotten the big 3 auto makers introuble. Guarenteed workforces at payrates that are the top of the industry.