At least two girls wearing leggings were barred from boarding a United Airlines flight on Sunday because they did not meet a dress code for special pass travelers, the company said in a statement on Twitter amid a social media furor. According to a series of tweets by another traveler, Shannon Watts, the girls were required to change or put dresses on over their leggings before they were allowed to board their flight from Denver to Minneapolis. "The passengers this morning were United pass riders who were not in compliance with our dress code policy for company benefit travel," the airline said on Twitter as the incident went viral on social media. Also watch: In another tweet made in response to a question from a social media user, the airline said: "Casual attire for ticketed passengers is fine. The passenger today was a United pass traveler and follow different guidelines." United pass travelers are typically company employees or family members of employees. The policy and United's defense of it on social media touched a raw nerve for many women and girls who have made leggings a staple in their wardrobes. The popularity of leggings has sparked criticism that they are inappropriate attire in certain circumstances and some schools have barred girls from wearing them to class. Social media lit up with outrage against the policy and the airline for its response to the initial outcry. Celebrities chimed in with humorous protests. "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 top," model Chrissy Teigen tweeted. United, the No. 3 U.S. airline by passenger traffic, did not immediately respond to a request for additional comment. Watts, the passenger who initially reported the dispute on Twitter, described one of the barred passengers as a 10-year-old girl wearing gray leggings. Watts said the girls were allowed to board their flight after changing or putting dresses over their leggings. "This behavior is sexist and sexualizes young girls," Watts said on Twitter. "Not to mention that the families were mortified and inconvenienced."