It's the biggest leggings fiasco since the see-through Lululemon debacle of 2013.
A day after United Airlines refused to allow two teenage girls onto a flight for wearing the stretchy, form-fitting pants, the Chicago-based carrier wants the world to know that its passengers are "welcome" to wear leggings — as long as they paid for their flight.
The incident highlights the little-known policy by most major airlines to require employees and their family and friends to abide by a more conservative dress code than the general public while in the air.
United has been on the defense since the girls, who were flying as friends or family of a United employee, were denied boarding on a flight from Denver on Sunday after a gate agent told them that their leggings were inappropriate.
That decision sparked swift outrage on social media, with critics calling the airline sexist and vowing to stop flying the carrier.
Celebrities, including comedian Sarah Silverman and actors Patricia Arquette and William Shatner, jumped into the fray to chastise the airline's handling of the "leggings incident."
"We need to be clear here—Are leggings inappropriate attire on your airlines?," Arquette asked in a Twitter post Sunday.
The dispute has even prompted an online petition, asking United to adopt a "less sexist" dress code. As of Monday afternoon it had collected about 1,100 signatures.
United responded by saying that regular-paying fliers are welcome to wear leggings aboard its flights. The rules, however, are different for employees or their families.
Airlines officials say employees must meet a higher standard because they represent the carriers in the eyes of the public.
"Our expectations are that we travel a bit smarter," said American Airlines spokeswoman Polly Tracey.
While the incident has turned in a PR nightmare, the silver lining may be that airlines nationwide are now making sure their dress codes reflect modern clothing trends — and that those rules are communicated more clearly, said Wendy Patrick, a business ethics lecturer at San Diego State University.
"You can bet that behind closed doors, every airline is reevaluating its standard on clothing for passengers flying on passes," she said.
On most U.S. carriers, employees and their families and friends can fly free or with a deep discount. But the employee passes come with a long list of conditions, such as who is eligible and when they can use the passes.
United declined to reveal the dress code for employees and pass holders. But an online site for airline employees said the list of "unacceptable attire" for United includes sleepwear, "form-fitting lycra/spandex tops, pants and dresses," attire that reveals a midriff or any type of undergarments, or clothing that is "provocative, inappropriately revealing or see-through."
American Airlines has similar language in its employee guidelines. It prohibits "clothing that is distracting or offensive to others, for example clothing that is overly revealing (such as extreme miniskirts, halter and bra tops, sheer or see-through clothing), swimwear or sleepwear."
A Southwest Airlines spokeswoman said the airline's policy for employees and their families and friends requires that they "present a clean, well-groomed and tasteful appearance."
Delta Airlines said it does not have an item-specific clothing policy for employee pass holders but asks that they use "their best judgment when deciding what to wear on a flight."
The dress code for the general traveling public is less specific. Interestingly, in recent years passengers themselves have criticized the sloppy clothing choices of fellow travelers.
A survey of more than 2,000 fliers by the travel review site Airfarewatchdog.com last year found that 59% of air travelers believe airlines have the right to kick a passenger off a plane for not dressing appropriately.
The rules for appropriate attire are spelled out in an airline's "contract of carriage," the detailed terms and conditions that airlines impose on every passenger who buys an airline ticket.
United's contract of carriage says passengers can be booted from a plane if they are "barefoot or not properly clothed."
American Airlines' contract of carriage says the carrier can remove passengers from a flight if they "are clothed in a manner that would cause discomfort or offense to other passengers or are barefoot."
Ultimately, airline representatives say, flight attendants and the pilot have the final say in what is "appropriate" dress for a flight.
Once relegated to the home or the yoga studio, leggings have become a staple of the athleisure fashion trend. Women and girls of all ages now don the skin-tight pants for virtually any occasion: while running errands, to school or for a night out on the town.
Four years ago, athletic wear brand Lululemon issued a massive recall of its black yoga pants after it was discovered that the pants were sheer; the pants were eventually brought back with "more fabric across the bum."
As for the more recent leggings incident, United Airlines says it has no plans to immediately change the dress code in response to the criticism.
"Our gate agent followed the guidelines perfectly," said United spokesman Jonathan Guerin. "The pass riders completely understood the reasons why they weren't allowed."
However, he added, "We regularly review our guidelines, so we'll continue to take a look at it."
Although employees who travel on passes are not outwardly identifiable to other passengers, Guerin said it is important that they follow the company dress code.
"It's about taking pride in the company that you work for," he said. "We don't find that following a few extra rules to fly for free really makes a difference."
4:15 p.m.: This article was replaced with a staff-written version.
10:40 a.m.: This article was updated with comments from a United spokesman.