religous holidays & employment

It depends on many factors such as are you an at will employee?  Do you have an employment contract?  Are other people allowed t otake off for religious holidays but you are not?  If the company is opened for business on Rosh Hashannah and other employees have to work, it may be possible for your employer to require you to work.  Many employers, hospitals, police and fire departments for example, all have to be open 24 hours a day 365 days a year and require employees to be present even on religious holidays.