19 C.F.R. § 123.31 Merchandise in transit.
(a) From one contiguous country to another. Merchandise may be transported in transit across the United States between Canada and Mexico under the procedures set forth in part 18 of this chapter for merchandise entered for transportation and exportation.
(b) From one point in a contiguous country to another through the United States. Merchandise may be transported from point to point in Canada or in Mexico through the United States in bond in accordance with the procedures set forth in §§ 18.1 and 18.20 through 18.24 of this chapter except where those procedures are modified by this subpart or subparts E for trucks transiting the United States, F for commercial traveler's samples, or G for baggage.