Covered Employers under Title VII (employs 15 or more employees who worked at least 20 weeks in the current year or last year) must accommodate employees who hold religious beliefs which mandate a certain dress or grooming practice, unless the accommodation would create an undue hardship. An example is a person wishing to wear a yarmulke.
It is sometimes difficult to know whether the religious accommodation would create an undue hardship, the Equal Employment Opportunity Commission (EEOC) has said that customer preference is not an undue hardship, so the employer cannot segregate the employee and then claim that they accommodated the employee’s religious rights. However, if the religious dress practice would create some type of workplace safety concern, then the employer would not need to accommodate as long as it is a legitimate undue hardship.
Also, the employer may not retaliate against an employee who has requested a religious accommodation nor can there be workplace harassment.