The U.S. Customs and Border Protection agency this week fully implemented a rule that mandates airlines disregard “X” gender markers on passports and instead input either “M” or “F” when processing passenger information.

The “X” gender marker became available to U.S. passport holders in 2022 under the Biden administration, designed to serve individuals who declare that their gender identity falls outside traditional binary categories. This option allowed people with non-binary, intersex, or other gender identities to obtain travel documents they thought more accurately reflected their identity.

The new Customs and Border Protection rule comes in compliance with Executive Order 14168, titled “Defending Women From Gender Ideology Extremism and Restoring Biological Truth to the Federal Government,” issued by President Trump’s administration in January. 

According to CBP’s release, “If the travel document presented by a traveler for an international flight to or from the United States has a sex indicator other than ‘M’ or ‘F’ or does not otherwise indicate the sex of the traveler, the carrier or the traveler should select either ‘M’ or ‘F’. Submitting ‘M’ or ‘F’ in the sex field, in place of the value reflected on the travel document, will not subject the carrier to penalty.”

In a statement reported by Reuters, the customs agency also said “foreign travelers’ gender as indicated on their passport and their personal beliefs about sexuality do not render them inadmissible to the United States.” 

The CBP enacted the policy on July 14, beginning a 90-day “informed compliance” window in which airlines could still mark “X,” rather than “M” or “F,” without issue. As of October 12, that window expired, and “entering a nonbinary gender marker will result in an error and need to be altered,” LGBTQ Nation reports, adding that airlines are now stuck “trying to guess a traveler’s gender assigned at birth.”

July Pilowsky, a scientist and U.S. citizen currently residing in Spain who uses he/they/she pronouns, told the Guardian that the new rule is already disrupting life.

“What CBP officers do when you show them your document [passport] at the border, is they look at the sex marker on your document. And based on what that sex marker says, they decide what you’re supposed to look like and what your body is supposed to be like,” Dr. Pilowsky told the UK paper.

One critic wrote on Threads that the new policy has only one intent. “Cruelty is the purpose,” the poster said.

Meanwhile, the White House said the July executive order does not invalidate issued passports, but when government-issued IDs are renewed, the documents must reflect the holder’s biological sex at birth. 

“They can still apply to renew their passport—they just have to use their God-given sex, which was decided at birth,” press secretary Karoline Leavitt said in a statement at the time. “Thanks to President Trump, it is now the official policy of the federal government that there are only two sexes—male and female.”