Diane von Furstenberg, president of the fashion industry’s leading trade group, is going all out to prevent underage girls from working the catwalks during New York Fashion Week. She’s ordered all members to demand proof of age.

The leading international fashion show was rocked last year after TheImproper reported that model Valerija Sestic, told more than a dozen designers including Tory Burch, Rodarte and Oscar de la Renta, that she was 16.

Her birth year is listed as 1996 on some model directories, which would have made her only 14, going on 15. Her management said she turned 16 in October.

Check out Valerija’s photos; click to enlarge.

Kylie Jenner, sister of reality TV personality Kim Kardashian, openly flouted the policy by walking in Avril Lavigne’s show at New York Fashion Week last year when she was 14.

The Council of Fashion Designers of America issued voluntary guidelines after model Hailey Clauson, then 15, walked in Von Furstenberg’s runway show in Feb. 2011. The designer said she was unaware, at the time, of her age.

While the CFDA is putting designers on notice about underage models, it is continuing to take a back seat on underweight models. The group has a voluntary program in place to educate designers about the signs of eating disorders among models.

Beyond that, designers are free to hire very thin model for the catwalk. Other fashion capitals such as Madrid and Milan have tried to enforce Body Mass Index minimums for the past several years with limited success.

Plus-size model Katya Zharkova, and a magazine dedicated to plus-size models, launched a campaign earlier this month to publicize the fashion industry’s demand for ultra-thin models. “Twenty years ago the average fashion model weighed 8 percent less than the average woman. Today, she weighs 23 percent less,” they claim.

The CFDA launched its Health Initiative at the height of an international debate about underweight models in 2007. New York Fashion Week kicks off Feb. 9.