Under federal law your employer must make a reasonable accomodation for your religious practices; to not work on Sundays. If the employer does not need you to work on Sundays, or can change your shift with another employee, then the employer must take such steps. The exception for the employe would be if to make such an accomodation for you would create an undue burden upon it. You can find more about religious discrimination at this web site by reading the section on Employment discrimination, then go to religious discrimination. Does this help?
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Mark B. Replogle