A question about seniority and being a college student

I'm sure some people can help me here. I am a 21 year old Democrat with very progressive views. I am currently in college balancing significant coursework with my new job. The job is at a union shop, and obviously I'm at the very bottom of the seniority list.

My managers know I am in school, so they made a special schedule to accommodate me. This schedule allows me to not work mandatory shifts on days when I have class. Unfortunately, some of the more senior members of the union are now objecting because they say I'm bypassing seniority to get certain shifts, which would violate the contract. I may have to resign, which would be a shame, because I really like the work and we make a decent wage with good benefits (thanks to the union).

Still, I'm having a crisis of faith. I always supported pro-labor politicians and I think right-to-work is a terrible idea. But can you blame me for feeling a bit jaded if a union forces me to lose a job that I like? Not sure what to think here. Also, the union folks might agree to make an exception, not sure yet. They're talking it over with management.