10 U.S.C. § 2201: Apportionment of funds: authority for exemption; excepted expenses

If the President determines such action to be necessary in the interest of national defense, the President may exempt from the provisions of section 1512 of title 31 appropriations, funds, and contract authorizations available for military functions of the Department of Defense. Upon a determination by the President that such action is necessary, the Secretary of Defense may provide for the cost of an airborne alert as an excepted expense under section 6301(a) and (b)(1)–(3) of title 41. Upon a determination by the President that it is necessary to increase (subject to limits imposed by law) the number of members of the armed forces on active duty beyond the number for which funds are provided in appropriation Acts for the Department of Defense, the Secretary of Defense may provide for the cost of such additional members as an excepted expense under section 6301(a) and (b)(1)–(3) of title 41. The Secretary of Defense shall immediately notify Congress of the use of any authority under this section.