Old Navy, the San Francisco-based clothing retailer, has responded to claims of sexism and size discrimination in a petition filed Tuesday accusing the company of charging more for its women’s plus-size jeans, while keeping costs uniform for men regardless of size.

The Gap Inc., which owns Old Navy, reportedly responded by saying that the price difference was based on the use of “unique fabrics and design elements” that are not found in men’s jeans. The petition urging the company to change its pricing policy has so far received more than 36,000 signatures. According to reports, Old Navy reportedly charges nearly $15 more for women's plus-sized jeans.

“For women, styles are not just larger sizes of other women’s items, they are created by a team of designers who are experts in creating the most flattering and on-trend plus styles, which includes curve-enhancing and curve-flattering elements such as four-way stretch materials and contoured waistbands, which most men's garments do not include,” Debbie Felix, a spokesperson for Gap, said in a statement, according to NBC's Today.

Renee Posey, the petition’s creator, gave an example of a size six Rockstar Super Skinny Jeans that was being sold for $27, while the same pair of jeans in size 26 cost $40. However, the same jeans type for men cost $25, regardless of the size.

“If they are charging plus-sized women more to cover the cost of the fabric being used, then why aren’t they doing the same for men?” Posey wrote in the petition, adding: “This is entirely unfair and offensive on many levels. For a company like Old Navy, who claims to be inclusive and strives to provide affordable clothing for everyone, this practice completely undermines their mission."