There is a Supreme Court case, either 1972 or 1974, that says you can not be granted an religious accommodation if you are violating a Union Contract. You may be in violation of seniority regarding the assignment of additional work/overtime if the work is moved to a senior person. I'll look for the case and get it for you. One of the guys in my Local tried to use it to get off every wednesday for bible study (or something) and was denied because it violated all senior drivers ability to get personal holidays or vacation. The guy had to choose to quit or accept that.