10 U.S.C. § 12302: Ready Reserve

In time of national emergency declared by the President after January 1, 1953 , or when otherwise authorized by law, an authority designated by the Secretary concerned may, without the consent of the persons concerned, order any unit, and any member not assigned to a unit organized to serve as a unit, in the Ready Reserve under the jurisdiction of that Secretary to active duty for not more than 24 consecutive months. the length and nature of previous service, to assure such sharing of exposure to hazards as the national security and military requirements will reasonably allow; family responsibilities; and employment necessary to maintain the national health, safety, or interest. Not more than 1,000,000 members of the Ready Reserve may be on active duty, without their consent, under this section at any one time.