If you can prove that the cut in hours was in direct response to your request and because of your request, then you could file a complaint with the EEOC -- or your comparable state agency-- for religious discriminaton.  If they cut your hours because the only other day they had for you to work was Sunday and you can't do that, then your complaint may or may not be successful.  They are required to accomodate your request for Sunday's off, but they are not required to give you make up days.  If your managers have made comments to each other or to other employees that they are trying to run you off because of your request, it would strengthen the presumption that your hours are being cut for an illegal reason.