The Advertising Standards Authority, the ad watchdog of the U.K., has banned an ad for the Parisian fashion house Yves Saint Laurent that it says showed an “unhealthily underweight” model. It called the ad “irresponsible.” The ad appeared in Elle U.K.

The spring 2015 ad from YSL designer Hedi Slimane shows 18-year-old model Kiki Willems in poses that highlight her long arms and legs. She is pictured in the black-and-white ad in a short, dark dress and platform high heels. The model’s pose and the lighting effect draw attention to her rib cage, which is “visible and appeared prominent,” the ruling found.

The ASA also said “her thighs and knees appeared a similar width, and ... looked very thin,” especially the “contrast between the narrowness of her legs and her platform shoes.” The agency said the ad may not appear again in its current form and called on advertisers to ensure images were created responsibly.

The ad is the latest in a long line of controversies surrounding the fashion industry’s use of thin models, among them the death from anorexia of French model Isabelle Caro following a shocking ad campaign and bans on ultra-skinny models in Israel and France. In response to the ruling, Yves Saint Laurent indicated it didn’t agree with the view that the model was unhealthily thin “but did not provide a detailed response,” the British agency said.

Both Elle U.K. and Saint Laurent declined to comment on the ban when CNN reached out to them. The Paris-based brand could come under heavy fines for employing an underweight model. In early April, the French Parliament passed a law banning the use of excessively thin fashion models.

Under the new legislation, models must present medical proof of a body mass index of at least 18 to be hired for a job. If fashion houses don’t adhere to the new rule, they can end up paying a fine of up to $82,000 and possibly six months' imprisonment.