(a) Any of the officers or persons authorized to board or search vessels may stop, search, and examine, as well without as within their respective districts, any vehicle, beast, or person, on which or whom he or they shall suspect there is merchandise which is subject to duty, or shall have been introduced into the United States in any manner contrary to law, whether by the person in possession or charge, or by, in, or upon such vehicle or beast, or otherwise, and to search any trunk or envelope
All articles brought into the United States by any individual must be declared to a CBP officer at the port of first arrival in the United States, on a conveyance en route to the United States on which a CBP officer is assigned for that purpose, or at a preclearance office in a foreign country where a United States CBP officer is stationed for that purpose. 19 C.F.R. §148.11 T.D. 73-27, 38 FR 2449, Jan. 26, 1973, as amended by CBP Dec. 09-37, 74 FR 48854, Sept. 25, 2009