Federal anti-discrimination law says you must offer reasonable accommodations to employees' "sincerely held religious beliefs or practices," as long as the accommodation wouldn't place an undue hardship on your organization. But how can you prove a belief is sincerely held? It's nearly impossible.
So, instead of becoming drawn into a messy dispute or lawsuit over whether a religious belief is sincere, it's typically smarter to err on the side of caution, and acceptance, and do your best to accommodate the employee's request.
As in the following case, your efforts to accommodate an employee's religious accommodation request, no matter how bizarre, will go a long way in building good will if the dispute lands in court.
Recent case: A Costco cashier claimed that her membership in the "Church of Body Modification" required her to wear 11 ear piercings and eyebrow piercings at all times.
Her employer's dress code banned visible facial piercings. Still, Costco twice offered her an accommodation; she could wear clear plastic retainers (spacers that would prevent the holes from closing up) or Band-Aids covering the piercing while on duty. She refused and chose not to come to work. Costco fired her, and she sued for religious discrimination.
A district court sided with Costco, saying it offered a reasonable accommodation. Covering piercings didn't infringe on the employee any more than wearing clothing to cover tattoos (which she had). Costco wisely chose to accommodate her belief rather than fighting a battle over whether her belief was "sincerely held." (Cloutier v. Costco Wholesale, No. 04-1475, D.Mass., 2004)
Online resource: For more details on accommodating re-ligious beliefs and avoiding religious-bias lawsuits, see the EEOC site on this topic at www.eeoc.gov/types/religion.html.