DENVER - United Airlines responded to criticism it received on Sunday after it barred two teenage girls from boarding a flight because they were wearing leggings. 

The incident sent a number of social media users into an uproar, with some calling the policy sexist and discriminatory against women.

The story came to light after Shannon Watts, an activist who witnessed the exchange at an airport in Denver, tweeted about it early Sunday.

1) A @united gate agent isn't letting girls in leggings get on flight from Denver to Minneapolis because spandex is not allowed?

— Shannon Watts (@shannonrwatts) March 26, 2017

The teenage girls were told by an employee at the gate agent that these aren't her rules and she only enforces them. The two girls, who weren't identified, "looked very panicked," according to Watts. 

A spokesperson for United said the two could not board a flight from Denver to Minneapolis because their leggings "were not in compliance with dress code policy for company benefit travel," a program that lets United workers and their family members travel free on a standby basis.

"There are different rules for these privileges because people are flying for free," he said in an emailed statement Sunday.

@baddestmamajama United shall have the right to refuse passengers who are not properly clothed via our Contract of Carriage. ^FS

— United (@united) March 26, 2017

United Airlines issued tweets in response to users who were upset about the incident. The company tweeted saying it reserves the right to deny service to "passengers who are not properly clothed via our Contract of Carriage."

United said the teens waited for the next flight and eventually got to travel under the benefit program. For "regular customers," the airline said in the statement, "leggings are welcome."