7 U.S.C. § 8305: Interstate movement

The Secretary may prohibit or restrict—(1) the movement in interstate commerce of any animal, article, or means of conveyance if the Secretary determines that the prohibition or restriction is necessary to prevent the introduction or dissemination of any pest or disease of livestock; and (2) the use of any means of conveyance or facility in connection with the movement in interstate commerce of any animal or article if the Secretary determines that the prohibition or restriction is necessary to prevent the introduction or dissemination of any pest or disease of livestock.