50 U.S.C. § 1701: Unusual and extraordinary threat; declaration of national emergency; exercise of Presidential authorities

(a) Any authority granted to the President by section 1702 of this title may be exercised to deal with any unusual and extraordinary threat, which has its source in whole or substantial part outside the United States, to the national security, foreign policy, or economy of the United States, if the President declares a national emergency with respect to such threat. (b) The authorities granted to the President by section 1702 of this title may only be exercised to deal with an unusual and extraordinary threat with respect to which a national emergency has been declared for purposes of this chapter and may not be exercised for any other purpose. Any exercise of such authorities to deal with any new threat shall be based on a new declaration of national emergency which must be with respect to such threat.