Employers have a duty to reasonably accommodate their employee’s sincere religious beliefs, unless it would cause undue hardship. The standard here is less onerous than for accommodating a disability though. If an accommodation would require more than a minor cost, the employer does not need to provide it.
Accommodations for religious beliefs often take the form of changes to work schedules or dress codes. For example, if a Jewish employee requests not to be scheduled on Rosh Hashanah, the employer may need to schedule another available employee for work that day. Or, an employer may need to make an exception to a strict dress code to allow a Muslim woman to wear a Hijab.
Go to the main employment discrimination FAQ for employees page.