25 U.S. Code § 3733 - Cooperative agreement between Department of the Interior and Indian tribes
(a) Cooperative agreements
(A) To facilitate the administration of the programs and activities of the Department of the Interior, the Secretary may negotiate and enter into cooperative agreements with Indian tribes to—
(2) In cooperative agreements entered into under paragraph (1), the Secretary may advance or reimburse funds to contractors from any appropriated funds available for similar kinds of work or by furnishing or sharing materials, supplies, facilities, or equipment without regard to the provisions of section 3324 of title 31 relating to the advance of public moneys.
In any agreement authorized by this section, Indian tribes and their employees may perform cooperative work under the supervision of the Department of the Interior in emergencies or otherwise as mutually agreed to, but shall not be deemed to be Federal employees other than for the purposes of sections 2671 through 2680 of title 28 and sections 8101 through 8193 of title 5.