A Yves Saint Laurent ad has been banned in the U.K. by the country's advertising watchdog, which ruled that the model used appeared "unhealthily underweight."
The ad for the French luxury group, which ran in Elle magazine, showed a black and white photo of a woman lying on the floor in a short black dress, leather jacket and platform shoes.
Her ribs "appeared prominent," according to the Advertising Standards Authority (ASA) ruling released Wednesday. It added that the lighting and pose drew attention to the model's legs, "which looked very thin," and her thighs and knees appeared to be of a similar size.
"We therefore considered the model appeared unhealthily underweight in the image and concluded that the ad was irresponsible," the ASA, which provided CNBC with an image of the ad, said.
The ad was banned from appearing in its current form in the U.K.
Yves Saint Laurent didn't give a detailed response to the ASA, but indicated they didn't agree that the model was unhealthily thin.
Both Yves Saint Laurent and Elle UK gave no comment when contacted by CNBC.
Read MoreFashion brands withthe best resale value
Beat, a charity which supports those affected by eating disorders, said it was pleased that the ASA was "taking action to uphold their responsibility for the social impact of adverts."
"The constant portrayal of a very slender look as the only aspirational ideal for young people needs to be challenged if a generation are to grow up with a robust sense of their self-worth," a Beat representative told CNBC by email.
The ASA recently doled out a similar ruling to Urban Outfitters, for a photo used on the clothing retailer's website. A model wearing a pair of briefs in the lingerie section was described as "very thin," with a "significant gap between the models' thighs." The watchdog said it was concerned that the photo might be seen as aspirational by the company's young target market.
Urban Outfitters said it did not consider the model to be underweight or unhealthily thin, but instead had a "naturally tall and slim physique," the ASA said in a release.
Samantha Arditti, head of U.K.-based body confidence movement Be Real, told CNBC that ads like these piled pressure on people who already faced unachievable expectations around body size, and could lead to unhealthy and extreme approaches to weight loss.
"We need media, advertisers and publishers to use images that show a diverse range of models to reflect what we really look like so we can feel more confident about who we are" she added.