The latest travel ban appears to include yoga gear.

On Sunday, a United Airlines gate agent stopped two girls from boarding a flight from Denver to Minneapolis for wearing leggings, according to a live account of the debacle by Shannon Watts, a fellow passenger and founder of Moms Demand Action, a grassroots movement to end gun violence. “She’s forcing them to change or put dresses on over leggings or they can’t board,” she tweeted. “Since when does @united police women’s clothing?”

Responding on Twitter, United Airlines, a unit of United Continental Holdings UAL, -3.61% , tweeted that such decisions were at the discretion of a gate agent and said it has the right to refuse transport for passengers that violate Rule 21 of the airline’s contract of carriage. That rule says passengers may be denied if they “are barefoot or not properly attired.” It does not specify what constitutes proper attire; Watts noted that the father of one of the children was wearing shorts.

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Later Sunday, United tweeted at Watts again, saying the travelers in question were traveling on an employee and family of employee discount: “We appreciate you being our eyes and ears. The customers this morning were United pass travelers.” It added, “There is a dress code for pass travelers as they were representing UA when they fly.” That code states such travelers should be “well-groomed, neat, clean and in good taste.” United pass travelers typically travel on heavily discounted or free tickets, and comprise current and retired employees and their families. (United did not immediately respond to a MarketWatch request for comment.)

The debacle took off on social media with several boldface names joining in:

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And others took issue with United previously promoting yoga pants as travel wear. The Academy Award-winning actress Patricia Arquette was among those who took United to task, saying the airline should not have targeted young girls. The actress Chrissy Teigen tweeted: “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.”

Attire deemed “unacceptable” for pass travelers cites skirts and tops that reveal a midriff and Lycra/Spandex tops, pants and dresses — items, one might argue, likeliest to be worn only by women. The passengers may wear denim. Also, Watts said a man, who she said was the girls’ father, was allowed on the plane wearing shorts, suggesting that the policy was mostly aimed at the female dress code.

Some consumers understood why United would have a different policy for “pass” travelers, but others were not placated by the airline’s clarification: