United Airlines announced Friday it is now the first U.S. airline to provide customers non-binary gender booking options for flights.

“United is excited to share with our customers, whether they identify along the binary of male or female or not, that we are taking the steps to exhibit our care for them while also providing additional employee training to make us even more welcoming for all customers and employees,” Toby Enqvist, the carrier’s Chief Customer Officer, said in a statement.

According to United, the company is partnering with several LGBTQ non-profit groups, including the Human Rights Campaign and the Trevor Project, to train employees on the newly-announced booking options.

“By providing non-binary gender selection for ticketing and the gender-inclusive honorific ‘Mx’ in user profiles, United Airlines is taking an important step forward for non-binary inclusion,” Beck Bailey, who leads the Human Rights Campaign’s Workplace Equality Program, said.

In a separate statement, Trevor Project CEO Amit Paley, said of the move by United: “We are thrilled to bring Trevor’s expertise on the mental health of LGBTQ people to United to ensure its employees maintain safe and inclusive spaces for LGBTQ employees and guests.”

The development follows the approval of international best-practices for servicing flight customers using “non-binary IDs” by both trade groups the International Air Transport Association and Airlines for America.

Other major U.S. airlines, including Delta and Southwest, have previously stated they are also mulling introducing similar booking accommodations for “non-binary” customers, but have not offered a proposed roll-out date.

“Please know that while we don’t have a timeframe to share, Southwest is currently investigating solutions and the technical requirements needed to provide our customers non-binary gender marker options during the booking process,” Southwest spokeswoman Michelle Agnew told USA Today.