DENVER (CBS NEWS) -- United Airlines has a message for its regular-paying customers: “your leggings are welcome.”

The Chicago-based airline sought to clarify its stance after a gate agent on Sunday barred two teenage girls from boarding a flight from Denver to Minneapolis -- an incident that sparked a deluge of online backlash from critics, including celebrities.

An airline spokesman said that the girls were traveling Sunday under an employee travel pass that includes a dress code.

“The passengers... were United pass riders and not in compliance with our dress code for company benefit travel,” United said in a statement on its website.

United pass riders are relatives or friends of United airline employees who can fly free or at heavily discounted travel rates, the airline said.

“When taking advantage of this benefit, all employees and pass riders are considered representatives of United,” the airline said. “And like most companies, we have a dress code that we ask employees and pass riders to follow.”

United said it regularly reminds its employees “that when they place a family member or friend on a flight for free as a standby passenger, they need to follow our dress code.”

“To our regular customers, your leggings are welcome,” United said.

That didn’t, however, appease some critics. Comedian Sarah Silverman suggested to United that it rethink its policy -- after she tweeted that she was changing all of her United bookings for an upcoming tour to other airlines. 

Delta, one of United’s competitors, also had some fun with the controversy, tweeting on Monday: “Flying Delta means comfort. (That means you can wear your leggings.)”