Stricter dress codes for employees' guests not uncommon among airlines

— -- United Airlines is under fire for barring two teenage girls from their flight because they were wearing leggings -- but the policy United is citing is not uncommon among airlines.

In a statement on its website, the airline said that when employees and their guests utilize the benefit of free or discounted travel, they are seen as representatives of the airline itself and therefore must abide by a stricter dress code.

“When taking advantage of this benefit, all employees and pass riders are considered representatives of United,” the statement reads. “And like most companies, we have a dress code that we ask employees and pass riders to follow. The passengers this morning were United pass riders and not in compliance with our dress code for company benefit travel.”

Rick Seaney, CEO of FareCompare, a website that curates deals on flights from around the world, said this type of dress code restriction is common for guests of employees who are receiving free travel.

“These tickets have a stricter dress code than the normal contract of carriage,” Seaney told ABC News.

Seaney said trouble can arise when it comes to interpreting these dress codes.

“Generally the problem with ‘judgment’ calls are that every gate agent [and] flight attendant ends up being the judge and jury,” Seaney, who is also a travel columnist for ABC News, said, adding that each individual’s interpretation of the rules can result in uneven application.

Despite the fact that this practice may be commonplace among airlines, some are still criticizing the policy as outdated and sexist.

Southwest Airlines said that although they do not have a dress code for regular paying customers, they do hold employees and their guests to higher standards.

“Our Employee Travel Privilege Policy does require employees and guests of employees to present a clean, well-groomed and tasteful appearance,” a representative for Southwest told ABC News.

A representative for American Airlines also told ABC News that in addition to a dress code policy for paying customers, they too have an internal dress code policy for guests of employees.

JetBlue also has a specific policy for these guests.

"As is common across airlines, JetBlue crewmembers and their friends and relatives flying with free flight passes are asked to maintain certain minimum dress standards and be well-groomed at all times," a representative for JetBlue told ABC News, adding that the full internal dress code is not available publicly but is easily accessible to employees to share with their guests. "All of our crewmembers must complete a training on free pass riding, which includes the dress standards."

United’s statement noted that the airline regularly reminds employees of the necessary dress code their guests must follow. Flip-flop sandals and ripped jeans are also among prohibited items for employees and their guests who utilize travel benefits, "Good Morning America" reported.

“To our regular customers, your leggings are welcome,” the statement concludes.