Federal law says you must grant employees "reasonable accommodations" for their religious beliefs and practices. But that doesn't mean that any employees who are told they must work on their Sabbath have an automatic lawsuit.
To move their case along in court, employees must show that they suffered an "adverse employment action" (such as being fired, transferred or demoted) due to their religious accommodation request.
Employers can face liability if they tell employees to work and then fire the employee for refusing. Employees who quit rather than work can also sue. But employees who simply work and grumble about it cannot.
Recent case: Shirley Martin worked for Wal-Mart in Dallas and was a minister in her church. She asked for Saturdays and Sundays off, but her manager told her she had to work. She did, but later sued, alleging failure to accommodate her religious beliefs.
The federal court dismissed the case, reasoning that only people who are actually fired, demoted or otherwise subjected to an adverse employment action can allege religious discrimination. In other words, Martin could sue only if she had quit or been fired after refusing to work. (Austin v. Wal-Mart, No. 3:05-CV-1687, ND Texas, 2006)