DALLAS >> American Airlines is adding “U” and “X” options for gender when passengers buy tickets, joining a growing number of entities recognizing choices beyond simply male and female.

American Airlines passengers can now change to “U” or “X” designations by talking to a customer service agent on the phone. American is also in the process of making the change to its website, too. “U” stands for unspecified or undisclosed and X has become a standard marker for those that don’t identify as male or female.

“We recently completed system updates in an ongoing effort to offer nonbinary gender selections,” American Airlines spokeswoman Stacy Day said in a statement. “Taking care of our customers and team members is what we do, and we are glad to be able to better accommodate the gender preferences of our travelers and team members.”

But Fort Worth-based American Airlines is urging passengers to stick with the gender on government­-issued driver’s licenses or ID cards, even if it doesn’t match personal preferences. That’s because booking information needs to match details in federal databases for use in TSA security lines.

Airlines are required by TSA passenger data systems to report a gender when customers buy a ticket. Now, those systems only give the option to mark male or female.

United Airlines was the first major airline to make the adjustment earlier this year.

Southwest Airlines is also looking at changes but isn’t sure when that will come.

“Please know that while we don’t have a time frame to share, Southwest is currently investigating solutions and the technical requirements needed to provide our customers nonbinary gender marker options during the booking process,” said a statement from Southwest spokeswoman Ro Hawthorne.

Companies such as American and Southwest are increasingly trying to find ways to accommodate a more visible population that doesn’t identify as strictly male and female.

In the last few years, there has been a growing awareness for individuals who identify as a gender different than the sex assigned at birth, as both male and female, neither gender or something in between.

American spokesman Ross Feinstein said the change was prompted partly by a growing number of states and foreign countries issuing driver’s licenses and other identification with “X” options for gender.

In the U.S., 19 states allow individuals to select “X” for gender on identification. U.S. passports also only have a male and female option.

Gender identity can be particularly difficult for individuals at the airport, said Leslie McMurray, a transgender education and advocacy coordinator at The Resource Center, an LGBTQ advocacy organization in Dallas.

“Flying is always an adventure and it starts with TSA,” said McMurray, a transgender female. “There is a boy button and girl button. If it doesn’t match, it starts problems.”

TSA scanning equipment is specified for males and females, giving better guidance to screeners for underwire on bras or contraband that might be stuffed in underwear or bras.

The TSA gives guidance to screeners for transgender individuals and options for pat-downs in lieu of machine screening. TSA spokesman Mark Howell said he’s not sure if the agency is making changes to its data systems to allow more gender options.

McMurray applauded American’s move, saying it could help make life easier for people who aren’t comfortable being labeled as male or female, even if the airport process isn’t perfect.

Airlines are required by TSA passenger data systems to report a gender when customers buy a ticket. Now, those systems only give the option to mark male or female.