Secretary of State Marco Rubio on Wednesday directed the State Department to suspend all passport applications seeking to change gender markers and all applications requiring an "X" gender marker, according to a memo seen by NBC News.

The memo cites an executive order President Trump issued hours after taking office, declaring that the U.S. government would recognize only two genders, male and female, and that “these genders are immutable and based on fundamental and indisputable Reality".

“The executive order provides that government-issued identification documents shall refer to an individual’s immutable biological classification as male or female,” Rubio’s memo states. “In agency documents, ‘sex’ should be used instead of ‘gender.’ To further clarify, it is U.S. policy that an individual’s gender is immutable.”

As a result, the Department of State will no longer issue an "X" gender marker in U.S. passports or birth records to U.S. citizens born abroad, the memo continues. It directed staff to suspend all applications requesting an "X" gender marker or gender marker change, adding that staff should not "take any further action" on these applications "pending further guidance from the department."

The memo applies to all applications currently in progress as well as any future applications, the memo states, adding that guidance on existing passports containing the "X" gender marker "will be provided through other channels."

In an email to NBC News, the U.S. State Department confirmed that it "will no longer issue U.S. passports bearing the related.

The spokesperson did not respond to questions about whether passports currently marked with an "X" are still valid, or what happens to people traveling with them, but said an update is imminent and will be shared on the department's travel website as soon as possible.

The uncertainty about how Trump's executive order will affect passports has caused fear and confusion among some transgender people, who shared on social media that they were processing passport renewal applications with the State Department.

Amy has a transgender son and asked that her first name be used to protect her family's privacy. She said she submitted an application to correct the gender marker on her teenage son's passport, which arrived on Tuesday, according to postal service tracking. She said she has called every day since then to check on its status, and as of Friday afternoon, all employees she had spoken to told her they were processing requests to update gender markers as usual. However, upon hearing the news of Rubio's memo, she said she was "devastated."

She worries that her son's passport application will be put on hold and his valid passport, which contains his previous legal name and gender marker and was sent as part of the application, will be held at a processing center, at least until the State Department issues new guidance.

“We filled out these forms so that everyone in our family had a valid passport because it suddenly became very necessary,” she said, noting that access to gender-affirming care for minors is changing rapidly across the country. "We don't know if we need to leave the country to get medical care and to have our son's valid passport withheld with no indication of when we will get it back feels illegal and scary."

A day after Trump pledged to ban gender-affirming care for minors nationwide, issuing an executive order on gender, the department removed a page from its website titled "Choose Your Gender Marker." The page, which still appears in Google search results, indicates that people applying for or renewing passports can choose male (M), female (F), unspecified, or another gender identity (X) as the gender marker on their U.S. passport book.

"We promote freedom, dignity, and equality for all people, including LGBTQI+ individuals," the page states. "We are demonstrating this commitment to better serving all U.S. citizens regardless of gender identity."

The now-deleted page also provided information about travel for LGBTQ people and warned that those with the "X" gender marker may not be able to travel to all countries. As of Tuesday afternoon, the page redirected to a regular passport information page.

Trump's executive order on gender and identity documents reverses two policies introduced by the Biden administration: one that allows transgender people to change the gender on their passports without providing proof of transition, and another that allows people who are intersex or Applicants who are neither male nor female select the “X” gender marker.