28 C.F.R. § 548.18
Consistent with maintaining security, safety, and good order in the institution, the Warden shall endeavor to facilitate the observance of important religious holy days which involve special fasts, dietary regulations, worship, or work proscription. The inmate must submit a written request to the chaplain for time off from work to observe a religious holy day. The Warden may request the chaplain to consult with community representatives of the inmate's faith group and/or other appropriate sources to verify the religious significance of the requested observance. The chaplain will work with requesting inmates to accommodate a proper observance of the holy day. The Warden will ordinarily allow an inmate to take earned vacation days, or to make up for missed work, or to change work assignments in order to facilitate the observance of the religious holy day.
28 C.F.R. § 548.18