19 CFR 148.22: Examination of air travelers' baggage in foreign territory.

(a) Examination and surrender of declaration. When places have been established in a foreign country where U.S. Customs officers have been stationed for the purpose of conducting Customs inspections and examinations (see §§ 101.5 and 162.8 of this chapter), persons destined to the United States on flights shall present themselves to those officers for inspection and examination of their baggage which may be passed in accordance with § 148.23 prior to boarding the flight. They shall comply with all U.S. Customs laws and other civil and criminal laws of the United States relating to importation of merchandise, including baggage, to the filing of false or fraudulent statements, and to the unlawful removal of merchandise from Customs custody, in the same manner as if the passengers, were arriving at an airport within the Customs territory of the United States. When baggage is examined in foreign territory, the baggage declaration shall be surrendered to the Customs officer at the airport of departure for the United States prior to boarding the flight.

(b) Subsequently acquired articles. When a person whose baggage has been examined and passed in foreign territory in accordance with paragraph (a) of this section subsequently acquires additional articles prior to return to the United States, the Customs officer to whom the declaration was surrendered may permit the amendment of that declaration to include the additional articles.