DENVER (AP) — Two teenage girls were barred by a gate agent from boarding a United Airlines flight from Denver to Minneapolis on Sunday because they were wearing leggings, according to a spokesman for the airline.

The girls, whose ages were not specified, were not allowed onto the morning flight because they were traveling under an employee travel pass that includes a dress code, United spokesman Jonathan Guerin said.

The dress code bars pass travelers from wearing spandex or Lycra pants such as leggings. The teenagers agreed to change their clothing and take a later flight, Guerin said, but the airline’s actions sparked a quick backlash on Twitter.

Activist Shannon Watts of Denver tweeted that she witnessed Sunday’s events and questioned United’s decision to police women’s clothing.

Watts said the girl’s father was allowed to board while wearing shorts and called the airline’s policy sexist.

Regularly ticketed passengers are not subject to the same dress code and can wear leggings, Guerin said. But the airline was standing by its policy for pass travelers because they are essentially representing the company, he said.

“We would ask the same of pass riders who were wearing flip-flops or who were wearing clothing that revealed their undergarments or torn, tattered jeans,” Guerin said.

AP