19 U.S.C. § 1461: Inspection of merchandise and baggage

All merchandise and baggage imported or brought in from any contiguous country, except as otherwise provided by law or by regulations of the Secretary of the Treasury, shall be unladen in the presence of and be inspected by a customs officer at the first port of entry at which the same shall arrive; and such officer may require the owner, or his agent, or other person having charge or possession of any trunk, traveling bag, sack, valise, or other container, or of any closed vehicle, to open the same for inspection, or to furnish a key or other means for opening the same.