United Airlines now offers customers options other than “male” and “female” to identify as when booking flights, the air carrier announced Friday.

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Customers can now identify themselves as M(male), F(female), U(undisclosed) or X(unspecified), corresponding with what is indicated on their passport or identification, United said in a statement.

Travelers can also be called the gender-neutral title “Mx.” during booking and in MileagePlus customer profiles, United officials said.

"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,” said United's Chief Customer Officer Toby Enqvist.

The airline said it worked with LGBT groups, the Human Rights Campaign and the Trevor Project on employee training initiatives.

The Transportation Security Administration currently requires passengers to disclose their gender identification prior to flying. A section of the TSA website dedicated to transgender passengers says screening is conducted "without regard to a person's race, color, sex, gender identity, national origin, religion or disability."

The TSA encourages passengers to book flights using the same name, birth date and gender listed on their government-issued ID. More states and jurisdictions are offering gender-neutral options on IDs, including California, Minnesota, Oregon and Washington, D.C., The Washington Post reported.