I think the rules vary among different variations of Judaism. The list of what strictly orthodox Jews are not allowed to do during Shabbat is long and to non Jews most of it may seem ridiculous. So called 'reformed' Jews may be less strict in following rules they see as decided by men (rabbis) and not God. So it will vary at times. I do think most thoughtful employers do accommodate the religious traditions of their Jewish employees as much as they can.
It isn't always easy for a non Jew to get straight forward answers on religious beliefs from a Jewish person. I was teaching a course on JudeoChristian history one time and a student asked, "How does a Jew know when the Sabbath begins on a cloudy day?" (Shabbat begins at sundown on Friday.) I didn't know and went to some Jewish chatrooms to get some answers. I was considered a malicious Christian troll however and was pretty severely verbally pummeled until I left.
This was on AOL with instant messaging though and one Jewish gentlemen did message me and determined I wasn't a troll. He explained that in his family, Shabbat began when the Sabbath meal was on the table Friday evening. Simple solution.
I wish now I had asked about how Jews should handle being asked or required to go to their jobs on the Sabbath. I didn't think about it at the time.