19 U.S.C. § 1582 : US Code - Section 1582: Search of persons and baggage; regulations

      The Secretary of the Treasury may prescribe regulations for the
    search of persons and baggage and he is authorized to employ female
    inspectors for the examination and search of persons of their own
    sex; and all persons coming into the United States from foreign
    countries shall be liable to detention and search by authorized
    officers or agents of the Government under such regulations.