Unions are like everything else. They have their good and bad. For every nightmare encounter with a union, we've also had an encounter without a hitch. Many guys in the union are not fanatics and realize the world isn't all union.

My advice is that if a union guy asks you if you are union, just say "no, unfortunately there is no union that exists for my field but luckily I work for a company that pays well and takes really good care of us". That may not stop the fanatics from cutting your wires, but it will go a long way towards establishing peace with some of the guys on the job if they realize there is no union for what you do and that your company isn't one of their "enemies".