According to a family friend who worked for the UAW (the huge American auto workers union) the answer to this is yes. I suspect the answer is actually "it depen

According to a family friend who worked for the UAW (the huge American auto workers union) the answer to this is yes. I suspect the answer is actually "it depends", but I don't know of any documented examples of unions whose members are allowed to make a separate peace. There are people in the comments who it sounds like have done so, perhaps they can weigh in on the mechanism.