After choosing former New Look shop assistant Katie Green for its "real" women campaign Wonderbra suggested that she sign with Premier Model Management, which also has Kelly Brook and Myleene Klass on its books.
The agency told Green that despite being selected for the ads because of her curves the normal size for models was size 8 to 10 and that she needed to lose two stone.
Green said: "It's been very hard for me. They told me that I had to lose weight and be like the other models or I was finished, so I decided to quit. I did not want to sacrifice my health or happiness."
Wonderbra selected Green, who is 5ft10, a healthy size 12 and weighs 10st 5lb, following a nationwide search for "real" women to appear in an ad campaign for its larger bra sizes.
In August Wonderbra unveiled a mosaic of thousands of "real" women photographed during the search to form an overall image of a close-up of Green's bust.
Copy for the poster read: "D-G. Because we're more than a handful." and was intended to capture both the brand's playful tone and the attitudes of the women who took part.
A spokesman for premier Model Management said: "We advised Katie that commercial and lingerie models need to be an average size 10 as is requested by the market sector she wanted to model for.
"This is a healthy size that can be achieved through exercise and good nutrition."