Department of Homeland Security and U.S. Customs and Immigration Services employees will no longer be able to process applications that contain an "X’ marker for gender.

A letter to DHS field operations and USCIS employees obtained by Fox News Digital advises officials to "not make a final decision on any application that would produce a document with an "X" marker, citing President Donald Trump’s January 20 executive order that "prohibits using the ‘X’ marker on our documentation and in our systems."

"This is consistent with President Trump’s executive order that the U.S. recognizes two sexes, male and female," DHS Assistant Secretary for Public Affairs Tricia McLaughlin told Fox News Digital. "This is common sense."

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The letter comes after Trump signed an executive order on his first day in office aimed at shifting the language used by the federal government in documentation, including a move to replace the term "gender" with "sex" on official documents.

"The erasure of sex in language and policy has a corrosive impact not just on women but on the validity of the entire American system. Basing Federal policy on truth is critical to scientific inquiry, public safety, morale, and trust in government itself," the order signed by Trump states.

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The move also reverses changes made during the Biden administration, including giving Americans who do not identify with either of the two biological sexes the option to mark documents such as passports with an "X" instead of "male" or "female."

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But Trump’s order calls for all federal agencies to ensure that all documents "accurately reflect the holder’s sex," which the order defines as "an individual’s immutable biological classification."

A new interim director has been tapped to lead the Federal Bureau of Prisons (BOP) as President Donald Trump looks to enforce a crackdown on transgender inmates in facilities that do not match their biological sex. 

William W. Lothrop was named the new BOP director after Colette Peters resigned on Inauguration Day. It's unclear when the Trump administration will appoint someone to permanently fill the role. 

"As we face ongoing challenges, including staffing shortages and operational issues, I am committed to working alongside you to find real solutions that strengthen our facilities," Lothrop said in the statement. "We will continue collaborating with our law enforcement partners and stakeholders to maintain robust programming and support services for inmates."

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On his first day in office, Trump announced a temporary hiring freeze for federal positions and reversed former President Joe Biden’s ban on private prisons. His executive order, "Defending Women from Gender Ideology Extremism and Restoring Biological Truth to the Federal Government," defines sex strictly as male or female, based on biological characteristics, and mandates that federal agencies adopt this definition in their policies and practices.

The order specifies that individuals should be housed in federal prisons according to their biological sex rather than their gender identity, which will apply to the 2,300 transgender inmates currently housed in federal prisons across the U.S. It also halts federal funding for transgender procedures and treatments for inmates.

"The Attorney General shall ensure that the Bureau of Prisons revises its policies concerning medical care to be consistent with this order, and shall ensure that no Federal funds are expended for any medical procedure, treatment, or drug for the purpose of conforming an inmate’s appearance to that of the opposite sex," the order reads.

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During the Biden administration, several U.S. states implemented policies allowing transgender inmates to be housed in facilities that align with their gender identity. In 2021, California became the first state to enact a policy permitting transgender inmates to request housing based on their gender identity. Since then, the state has seen a significant increase in such requests, with a 234% rise in the transgender inmate population.

In January 2022, New York state revised its policies to allow transgender individuals to choose their prison housing. And Colorado reached a legal settlement to house biological men in women's facilities last year, which was part of a case involving 400 transgender women. 

Fox News Digital has previously reported multiple cases of male inmates, serving sentences for sexual assault, murder and other violent offenses, in federal prisons being transferred to women’s facilities. Many of them have received taxpayer-funded medical procedures to medically transition genders.

Lothrop, who was formerly the BOP deputy director, is replacing Peters, who was appointed by then-Attorney General Merrick Garland in 2022 and touted as a reform-minded outsider tasked with rebuilding an agency plagued for years by staff shortages, widespread corruption, misconduct and abuse.

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The agency has nearly 36,000 employees and is responsible for more than 155,000 federal inmates. The BOP director is not subject to Senate confirmation, according to the legal news service Law 360. During her tenure, Peters appeared before the House and Senate Judiciary Committees and spoke about the challenges the BOP faced, but she had trouble getting results. 

During the end of Trump's campaign, he pledged he would crack down on left-wing gender ideology and ran a successful ad campaign attacking his opponent, former Vice President Kamala Harris, for her role in ushering in sex change procedures for incarcerated people in California.

"Kamala is for they/them, President Trump is for you," the narrator of Trump's campaign advertisement said.

Fox News Digital has reached out to the White House and BOP for comment. 

Fox News Digital's Michael Dorgan contributed to this report. 

In his first week in office, President Donald Trump has charged ahead with a series of executive actions, fulfilling a key campaign promise to challenge "gender ideology" in American institutions and promote "biological truth" rooted in "fundamental and incontrovertible reality." 

Meanwhile, the Supreme Court is poised to rule on two significant gender-related cases this year, and Trump's new executive action could spell further controversy in the higher court.

Last week, SCOTUS agreed to hear Mahmoud v. Taylor, which would determine whether schools can force teachers to read LGBTQ books to elementary-age children despite parental objections. At issue is whether parents will have the right to opt their children out of such instructions.

"If the Supreme Court's doing its job, it shouldn't impact [the case decisions] at all," Heritage Foundation senior legal fellow Sarah Marshall Perry told Fox News Digital in an interview. "What Trump's executive order was is a statement of really what the policies are going to be for the executives going forward into the new administration. And he did exactly what [former President Joe] Biden did with his executive order expanding sex to include gender identity."

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Perry noted the separation of powers between the executive and judiciary branches, adding that while the executive is mostly a political entity, the judiciary is non-political. 

SCOTUS will be obligated to focus solely on the facts presented in the cases before them, she said, which "will include questions relative to the parameters of the parental rights guidance on school curriculums and exactly what constitutes curriculum for purposes of opt-out, whether gender medicine and age and medical-based restrictions that happen to impact individuals who are transgender is a violation of the Equal Protection Clause." 

She also pointed out that the executive order should not influence the Supreme Court's decision-making, adding, "The executive order should have absolutely no bearing on what the Supreme Court decides going forward."

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In another case that already had their oral arguments heard last year, Skrmetti v. U.S., the higher court is weighing whether the equal protection clause, which guarantees equal treatment under the law for individuals in similar circumstances, prevents states from banning medical providers from offering puberty blockers and hormone treatments to children seeking transgender surgical procedures. 

The Biden administration joined the lawsuit by filing a petition to the Supreme Court in November 2023.

"I think the American people are gratified that they've got a president who is common sensical, who recognizes biological reality, who recognizes the text of civil rights law and the rule of law itself, and now they're going to say we have someone who was willing to stand in the gap for us, including through the Department of Justice, if the cases get all the way to the Supreme Court," Perry said. "But parents should, and I think will, be involved to be able to bring more legal challenges."

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"I think this election really sort of rises to shift, not just politically, but for many people philosophically as well, because we recognize that America was sort of pulled back from the perilous brink on even understanding what it meant to be male and female, even understanding what it meant to live amicably in a pluralistic society," Perry said. "We are now, I think, thankfully, seeing a rebirth of those long-standing beneficial ideas."

Trump's executive order, signed on Inauguration Day and titled, "Defending Women from Gender Ideology Extremism and Restoring Biological Truth to the Federal Government," declares that the U.S. will recognize only two sexes — male and female — based on immutable biological characteristics. 

It prohibits the use of gender identity in legal and administrative contexts, mandates that federal agencies, including those overseeing housing, prisons, and education, adhere to this definition when enforcing laws and issuing regulations. The order directs changes to government-issued identification documents, bans the promotion of "gender ideology" in federal programs, rescinds previous executive actions that promoted gender identity inclusion and instructs federal agencies to eliminate guidance or regulations that conflict with the new policy.

Trump's executive order reverses the Biden administration's executive order titled "Preventing and Combating Discrimination on the Basis of Gender Identity or Sexual Orientation," signed in 2021, which directed federal agencies to interpret and enforce civil rights laws to prohibit discrimination based on gender identity and sexual orientation.