It depends on the nature of the job. If you are in position where you could work other days or hours while doing your job, they have to accommodate you. But if the nature of this job is that you have to work Friday night or Saturday during the day to do the job, they can insist you do the job--or terminate you if you can't work. For example: say you work in a company and position where there are several or even many people working different shifts, so they could move someone without a religious concern to cover Friday night through Saturday sundown and move you to a different shift--in that case, they have to.On the other hand, say you work as a waiter for a non-Jewish restaurant that has Friday night and Saturday lunch to early dinner as some of its most imporant shifts; they don't need a waiter who can't work those hours. In that case, since moving you to their slow days means you're not doing the job, they don't have to move you.It depends, therefore, on the position and whether you can be accommodated or not. If you can be accommodated, they need to accommodate you.