18 U.S.C. § 1692 : US Code - Section 1692: Foreign mail as United States mail

Search 18 U.S.C. § 1692 : US Code - Section 1692: Foreign mail as United States mail

Every foreign mail, while being transported across the territory
of the United States under authority of law, is mail of the United
States, and any depredation thereon, or offense in respect thereto,
shall be punishable as though it were United States mail.