10 U.S.C. § 12301

(a) In time of war or of national emergency declared by Congress, or when otherwise authorized by law, an authority designated by the Secretary concerned may, without the consent of the persons affected, order any unit, and any member not assigned to a unit organized to serve as a unit, of a reserve component under the jurisdiction of that Secretary to active duty for the duration of the war or emergency and for six months thereafter. However a member on an inactive status list or in a retired status may not be ordered to active duty under this subsection unless the Secretary concerned, with the approval of the Secretary of Defense in the case of the Secretary of a military department, determines that there are not enough qualified Reserves in an active status or in the inactive National Guard in the required category who are readily available. (b) At any time, an authority designated by the Secretary concerned may, without the consent of the persons affected, order any unit, and any member not assigned to a unit organized to serve as a unit, in an active status in a reserve component under the jurisdiction of that Secretary to active duty for not more than 15 days a year. However, units and members of the Army National Guard of the United States or the Air National Guard of the United States may not be ordered to active duty under this subsection without the consent of the governor of the State (or, in the case of the District of Columbia National Guard, the commanding general of the District of Columbia National Guard). (c) So far as practicable, during any expansion of the active armed forces that requires that units and members of the reserve components be ordered to active duty as provided in subsection (a), members of units organized and trained to serve as units who are ordered to that duty without their consent shall be so ordered with their units. However, members of those units may be reassigned after being so ordered to active duty. (d) At any time, an authority designated by the Secretary concerned may order a member of a reserve component under his jurisdiction to active duty, or retain him on active duty, with the consent of that member. However, a member of the Army National Guard of the United States or the Air National Guard of the United States may not be ordered to active duty under this subsection without the consent of the governor or other appropriate authority of the State concerned. (e) The period of time allowed between the date when a Reserve ordered to active duty as provided in subsection (a) is alerted for that duty and the date when the Reserve is required to enter upon that duty shall be determined by the Secretary concerned based upon military requirements at that time. (f) The consent of a Governor described in subsections (b) and (d) may not be withheld (in whole or in part) with regard to active duty outside the United States, its territories, and its possessions, because of any objection to the location, purpose, type, or schedule of such active duty. (g) (1) A member of a reserve component may be ordered to active duty without his consent if the Secretary concerned determines that the member is in a captive status. A member ordered to active duty under this section may not be retained on active duty, without his consent, for more than 30 days after his captive status is terminated. (2) The Secretary of Defense shall prescribe regulations to carry out this section. Such regulations shall apply uniformly among the armed forces under the jurisdiction of the Secretary. A determination for the purposes of this subsection that a member is in a captive status shall be made pursuant to such regulations. (3) In this section, the term “captive status” means the status of a member of the armed forces who is in a missing status (as defined in section 551(2) of title 37 ) which occurs as the result of a hostile action and is related to the member’s military status. (h) (1) When authorized by the Secretary of Defense, the Secretary of a military department may, with the consent of the member, order a member of a reserve component to active duty— (A) to receive authorized medical care; (B) to be medically evaluated for disability or other purposes; or (C) to complete a required Department of Defense health care study, which may include an associated medical evaluation of the member. (2) A member ordered to active duty under this subsection may, with the member’s consent, be retained on active duty, if the Secretary concerned considers it appropriate, for medical treatment for a condition associated with the study or evaluation, if that treatment of the member is otherwise authorized by law. (3) A member of the Army National Guard of the United States or the Air National Guard of the United States may be ordered to active duty under this subsection only with the consent of the Governor or other appropriate authority of the State concerned.