25 C.F.R. § 1000.408
A Tribe/Consortium and its employees may use Federal supply sources (including lodging, airline, interagency motor pool vehicles, and other means of transportation) that must be available to the Tribe/Consortium and to its employees to the same extent as if the Tribe/Consortium were a Federal agency. While implementation of this provision is the responsibility of the General Services Administration, the Department shall assist the Tribe/Consortium to resolve any barriers to full implementation that may arise. While implementation of this provision is the responsibility of the General Services Administration, the Department shall assist the Tribes/Consortia to resolve any barriers to full implementation that may arise to the fullest extent possible.
25 C.F.R. § 1000.408