Airlines are planning to present travelers who don’t identify as either male or female more options when they book their flights.

Airlines for America, an industry group that represents some of the largest U.S. carriers, including American Airlines, JetBlue Airways and Alaska Airlines, and the International Air Transport Association, which represents most of the world’s airlines, recently approved standards for nonbinary passenger identification.

The changes aim to bring airlines in line with nonbinary identification cards so that travelers’ reservations match their IDs. Several states including California and Oregon offer nonbinary options on identification cards and other documents.

United Airlines in the coming weeks will allow travelers to choose from four options when they book their tickets: male, female, undisclosed and unspecified. Travelers who do not identify with a gender will be able use the tile “Mx,” said Maddie King, a United spokeswoman. The measures aim to ensure that “all of our customers feel comfortable and welcome no matter how they self-identify, which is why we will begin offering our customers the ability to select the gender with which they most closely identify during the booking process.”

Delta Air Lines, which is not a member of the trade group, said in a statement that it plans to add a nonbinary gender option to its booking page. Southwest Airlines is considering adding the option as well.