United Airlines on Friday announced it's become "the first U.S. airline to offer non-binary gender options throughout all booking channels" as well as the option to choose the title "Mx."

Now customers can "identify themselves as M(male), F(female), U(undisclosed) or X(unspecified), corresponding with what is indicated on their passports or identification," the airline said in a news release.

"United is determined to lead the industry in LGBT inclusivity, and we are so proud to be the first U.S. airline to offer these inclusive booking options for our customers," United Chief Customer Officer Toby Enqvist said in the release. "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."

More from the release:

As part of implementing these new changes, United has worked with the Human Rights Campaign and The Trevor Project on employee training initiatives. These initiatives include teaching employees about preferred pronouns and the persistence of gender norms, LGBT competency in the workplace and other steps to make United an inclusive space for both customers and employees.

"At the Human Rights Campaign, we believe being acknowledged as the gender you identify with is part of treating everyone with dignity and respect," Beck Bailey, acting director of the Workplace Equality Program, noted in the release. "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."

What was the reaction?

While some reacted positively to United's announcement, a number of Twitter users questioned the necessity of bringing gender into flight booking in the first place: "Why include gender at all in the process?" one user wondered. "We're all just packing into a tiny sky tube together for a few hours; why do you need to know what's in my pants first?"

Others unleashed sarcasm in response to the airline's non-binary gender options:

"It's so bizarre. 'Fly with us, we will participate in your delusion.' Strange times."

"Step 1: Look in your pants. Step 2: Identify if its more inny or outy. Step 3: If unsure consult your government issued birth certificate. Step 4: Check one of ONLY two REAL scientifically sound options 'Male/Female'. If still confused see Genesis 5:2 and a biology 101 book ASAP."

"I identify as a shape-shifting reptile, and I demand a window seat."

"As a self-identified Apache helicopter I am outraged at this discrimination against my gender."

"I identify as an emotional support pet & I would like to fly for free with my owner!"

"Just ask the TSA what I am; they probably spent the last 30 minutes feeling me up."

"I identify as a customer of an other airline."

Anything else?

The five biggest U.S. airlines — American, Delta, United, Southwest, and Alaska — all have told USA Today they plan to implement a suggestion by a pair of large trade groups to accommodate travelers using "non-binary IDs."