A woman was banned from Qantas Airways frequent-flyer lounge Wednesday for wearing UGG boots. The Australian airline qualified UGG boots as casual sleepwear, which is a prohibited under Qantas' dress code guidelines from being worn in its lounge.

Joanne Catherall, singer from The Human League, was denied entry into Qantas' lounge. A Qantas worker at the airline's Melbourne Airport's lounge prohibited her from entering and suggested that she go to a nearby shop to purchase more suitable footwear.

"Denied access @Qantas business class lounge in @Melair Melbourne Airport apparently Ugg (Australia) Boots are deemed sleepwear by the lady working there although no problem in any of the other lounges so far,"  Catherall said Wednesday on Twitter. "Helpfully she suggested I go to one of the shops & purchase some shoes."

Two days later, Catherall tweeted: "Me & my Uggs didn't even bother with the @Qantas lounge this morning at Sydney airport."

Qantas acknowledged Catherall's incident, but it didn't issue an apology. The airline remained "consistent" on standing by its strict dress code.

"We endeavor to remain consistent and uphold our Lounge's dress guidelines to all our guests," Qantas wrote on Twitter. "We don't accept them in our lounges as you can see on the dress-guidelines."

Sleepwear, including UGG Boots and slippers, are listed as a banned clothing item on Qantas' Domestic Lounge. Revealing, unclean or torn clothing is also among the items of banned clothing. The lounge will "decline entry if some items of clothing are too casual or inappropriate," according to Qantas' website

"Our lounges are a place where you can sit back and relax before your flight," Qantas' website read. "To ensure an enjoyable experience when you're visiting our domestic Qantas Clubs and Business Lounges in Adelaide, Brisbane, Canberra, Melbourne, Perth and Sydney, we ask that you follow our smart casual dress guidelines."

Qantas isn't the only airline with a dress code as United Airlines banned two teenage girls from boarding a flight for wearing leggings. Hawaiian Airlines expects all customers to dress wearing adequate footwear, in addition to clothing that covers the upper and lower torso, according to its website.

There are airlines, like Delta Air Lines, that don’t have specific dress codes in place. Delta did, however, tweet that it encourages passengers to not wear "swimwear, sleepwear, or underwear as outerwear." Since Delta aims for customer comfort, passengers are permitted to wear leggings. 

Qantas This photo taken on August 23, 2017 shows a Qantas plane taking off from Sydney airport. Photo: Getty Images