THEY'RE a popular item of activewear but one airline has deemed leggings inappropriate and prevented two female passengers - one of them a child - from boarding a flight for wearing them.
United Airlines faced harsh criticism online after an account of their 'fashion police' actions went viral on social media.
Passenger Shannon Watts was at the gate at Denver in the US state of Colorado waiting to board a flight when she witnessed the bizarre incident and Tweeted her thoughts.
"A @united gate agent isn't letting girls in leggings get on flight from Denver to Minneapolis because spandex is not allowed," Ms Watts posted.
"She's forcing them to change or put dresses on over leggings or they can't board. Since when does @united police women's clothing? Gate agent for (flight) 215 at 7:55. Said she doesn't make the rules, just follows them. I guess @united not letting women wear athletic wear?"
The initial implication was that the clothing was unsafe because of the type of material but the airline later clarified that its decision was based on appropriateness.
However author Dana Schwartz later Tweeted that one of the passengers was a 10-year-old girl, writing: "Good luck to @united explaining why she looked too sexual."
The two passengers were later allowed to get on the plane after changing their clothing, Watts reported.
I have flown united before with literally no pants on. Just a top as a dress. Next time I will wear only jeans and a scarf.— christine teigen (@chrissyteigen) March 26, 2017
The document doesn't define "properly clothed", which drew further ire from Twitter users - including model Chrissy Teigen and actress Patricia Arquette.
Teigen wrote: "I have flown united before with literally no pants on. Just a top as a dress. Next time I will wear only jeans and a scarf."
United Airlines later clarified that the passengers were "pass travellers", meaning employees or members of their family who fly at a discounted rate.
In a statement to Us Weekly, they said: "The passengers this morning were United pass riders who were not in compliance with our dress code policy for company benefit travel."