There is a way out. I was blind sided by teamsters my first year at a regional. Dues were required from your first day off IOE, WITH NO REPRESENTATION. (Due to the fact that you are on probation for a year and they can't protect you.) Yes you were paying for contract enforcement or something.
I was told they couldn't petition to have me fired as long as I never paid the joining fee or a single due. Lucky for me I never had.
There is one option that I think may be your only LEGAL option to not to be a part of the union and not fear being fired (which has been done). You need to legally separate from the union and join a charitable organization and whatever your dues would be each month you need to contribute that amount to that organization. You will still need to pay any contract negotiation assessments but other than that you are free and clear from them.
I also knew that there was one guy who formed his own union and paid himself the dues. That might be a process though.