Whenever Congress determines that more units and organizations are needed for the national security than are in the regular components of the ground and air forces, the Army National Guard of the United States and the Air National Guard of the United States, or such parts of them as are needed, together with units of other reserve components necessary for a balanced force, shall be ordered to active duty and retained as long as so needed.
10 U.S. Code § 10103. Basic policy for order into Federal service
Amendment by Pub. L. 104–106 effective as if included in the Reserve Officer Personnel Management Act, title XVI of Pub. L. 103–337, as enacted on Oct. 5, 1994, see section 1501(f)(3) of Pub. L. 104–106, set out as a note under section 113 of this title.