On July 7, 2025, U.S. Customs and Border Protection (“CBP”) instructed airlines and other travel carriers on a new rule that they must submit "M" (male) or "F" (female) in the sex field of the pre-departure information they transmit to CBP through the Advanced Passenger Information System (APIS), even if the traveler's passport contains a sex indicator other than M or F or does not otherwise indicate the sex of the traveler. This new rule, which has been in practice since July 14, 2025, is based on Executive Order 14168, Defending Women from Gender Ideology Extremism and Restoring Biological Truth to the Federal Government.

Identifying only binary sex recognition changes the previous practice of airlines being able to list gender markers other than just “M” (male) or “F” (female)—including an “X” gender marker to CBP before a flight. Should a passenger’s passport list a gender other than M or F, the carrier will have its own way of deciding which gender to use. A mismatch between someone’s travel documents and airline records could mean extra questioning at US customs upon arrival, but CBP does note that the mismatch should not be treated as lying unless they are not able to confirm one’s identity or travel purpose.