Lululemon is taking Costco to court, accusing the retail giant of selling knockoffs of its popular leggings and workout gear under Costco’s Kirkland Signature brand.

In a lawsuit filed Friday, the luxury athletic wear company claims Costco is copying several of its signature designs and selling them at a fraction of the price, creating what Lululemon calls “an improper association” with its premium products. The company pointed to the popularity of hashtags like #LululemonDupes on social media, where shoppers share tips on buying cheaper lookalikes of the pricey brand.

“As an innovation-led company that invests significantly in the research, development, and design of our products, we take the responsibility of protecting and enforcing our intellectual property rights very seriously,” Lululemon said in a statement. The lawsuit argues Costco is illegally profiting from Lululemon’s reputation and design patents by trading on its “reputation, goodwill and sweat equity.”

Costco, known for its deeply loyal members and massive sales under the Kirkland Signature label, hasn’t responded to the allegations yet. The company has made a name for itself by offering private-label alternatives to everything from olive oil to batteries — and, apparently, yoga pants too.

For Lululemon, this fight is about protecting more than just leggings. The Vancouver-based company, which brought in more than $10 billion last year, has built its brand around high-quality, high-priced athleisure and a devoted customer base that’s willing to pay a premium.

It’s not the first time a big brand has clashed with retailers over “dupes,” but it’s a clear sign Lululemon intends to draw a line when it comes to defending its designs.