10 U.S.C. § 10215

(a) (1) Officers of the Army National Guard of the United States who are not on active duty— (A) may order members of the Army National Guard of the United States to active duty for training under section 12301(d) of this title ; and (B) with the approval of the Secretary of the Air Force, may order members of the Air National Guard of the United States to active duty for training under that section. (2) Officers of the Air National Guard of the United States who are not on active duty— (A) may order members of the Air National Guard of the United States to active duty for training under section 12301(d) of this title ; and (B) with the approval of the Secretary of the Army, may order members of the Army National Guard of the United States to active duty for training under that section. (b) Officers of the Army National Guard of the United States or the Air National Guard of the United States who are not on active duty— (1) may enlist, reenlist, or extend the enlistments of persons as Reserves of the Army or Reserves of the Air Force for service in the Army National Guard of the United States or the Air National Guard of the United States, as the case may be; and (2) with respect to their Federal status, may promote or discharge persons enlisted or reenlisted as Reserves of the Army or Reserves of the Air Force for that service. (c) This section shall be carried out under regulations prescribed by the Secretary of the Army, with respect to matters concerning the Army, and by the Secretary of the Air Force, with respect to matters concerning the Air Force.