28 C.F.R. § 551.16
(b) Expenses for a marriage ceremony in the institution shall be paid by the inmate, the inmate's intended spouse, the inmate's family, or other appropriate source approved by the Warden. The Warden may not permit appropriated funds to be used for the marriage ceremony, except for those inherent in providing the place and supervision for the event. Upon request of the inmate, Bureau of Prisons or community clergy, or a justice of the peace may be authorized to assist in a marriage ceremony at the institution.