25 U.S.C. § 1a

For the purpose of facilitating and simplifying the administration of the laws governing Indian affairs, the Secretary of the Interior is authorized to delegate, from time to time, and to the extent and under such regulations as he deems proper, his powers and duties under said laws to the Commissioner of Indian Affairs, insofar as such powers and duties relate to action in individual cases arising under general regulations promulgated by the Secretary of the Interior pursuant to law. Subject to the supervision and direction of the Secretary, the Commissioner is authorized to delegate, in like manner, any powers and duties so delegated to him by the Secretary, or vested in him by law, to the assistant commissioners, or the officer in charge of any branch, division, office, or agency of the Bureau of Indian Affairs, insofar as such powers and duties relate to action in individual cases arising under general regulations promulgated by the Secretary of the Interior or the Commissioner of Indian Affairs pursuant to law. Such delegated powers shall be exercised subject to appeal to the Secretary, under regulations to be prescribed by him, or, as from time to time determined by him, to the Deputy Secretary or to an Assistant Secretary of the Department of the Interior, or to the Commissioner of Indian Affairs. The Secretary or the Commissioner, as the case may be, may at any time revoke the whole or any part of a delegation made pursuant to this section, but no such revocation shall be given retroactive effect. Nothing in this section shall be deemed to abrogate or curtail any authority to make delegations conferred by any other provision of law, nor shall anything in this section be deemed to convey authority to delegate any power to issue regulations.