A British pop star has sparked a debate around whether UGG boots are sleepwear.

Joanne Catherall, a vocalist from the band the Human League, shared on Twitter on Dec. 13 that she was denied entry to the Qantas Airlines business-class lounge at the Melbourne Airport because she was wearing the Australian sheepskin-lined boots.

"UGG (Australia) Boots are deemed sleepwear by the lady working there although no problem in any of the other lounges so far," Catherall tweeted. "Helpfully she suggested I go to one of the shops & purchase some shoes."

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Qantas responded on Twitter with the statement: "Hi Joanne, we endeavour to remain consistent and uphold our Lounge's dress guidelines to all our guests. You may find details here: http://bit.ly/1TKrgMP."

Qantas specifically calls out UGG boots and identifies them as sleepwear in the domestic lounge dress guidelines that also deem thongs, bare feet, head-to-toe gym wear, and torn clothing inappropriate.

Catherall posted a followup tweet questioning the guidelines: "Why would an @UGG boot I wear outdoors in all weathers be classed as sleepwear in @Qantas lounge but nowhere else that I have ever been on this earth?"

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In the comments, many defended Catherall and criticized Qantas for enforcing a dress code.

"Why does it even matter to Qantas what people wear?" tweeted @isaaclibby. "Hilarious that somehow Uggs are sleepwear. What a joke company. Will avoid."

"I'm sorry but @Qantas this is pure snobbery," chimed in @bettycarlyle. "I always wear Ugg boots to travel in as they r so comfy & ive never not been allowed in a Lounge in America, Europe or the UK."

"Oh my goodness when would [you] go [to] bed in a pair of Ugg boots???" tweeted  Michelle Teale.

UGG Boots have been around in Australia since the 1960s and were adopted by surfers in the United States in the 1970s. Today, many love them because they're warm and comfortable, but some also find the boots unattractive and overly casual.

A commenter shared in response to a Fox News story covering the issue, "Good - [UGGs] are like flip-flops, fine for the beach or coming out of a shower but in public, uh no (ok, flip flops are fine for 8 year old girls or 3 year old boys) but after that, get some real shoes."