Nike Inc. escalated its legal battle with sneaker marketplace StockX, saying it purchased four pairs of counterfeit shoes on the platform despite the company’s promises that it is only marketing authentic footwear.The world’s largest athletic-wear maker asked a federal judge to let it add claims of counterfeiting and false advertising to the current trademark-infringement lawsuit against StockX.“Those four pairs of counterfeit shoes were all purchased within a short two-month period on StockX’s platform, all had affixed to them StockX’s ‘Verified Authentic’ hangtag, and all came with a paper receipt from StockX in the shoe box stating that the condition of the shoes is ‘100% Authentic,’” Nike said in a court filing Tuesday.StockX didn’t immediately respond to an emailed request for comment.Nike sued StockX in February in federal court in Manhattan, accusing the marketplace of “blatantly free-riding” on Nike’s trademarks and goodwill with a service called Vault NFTs. StockX argued that its NFTs aren’t digital sneakers but simply listings for physical sneakers that are stored in its vault and can be traded by users.Legal scuffles are breaking out over NFTs as they become more mainstream, attracting major brands ranging from Louis Vuitton to Taco Bell. Nike bought virtual sneaker maker RTFKT for an undisclosed sum in December, and launched its own digital shoes last month.StockX is said to be planning to go public as alternative assets like sneakers and collectibles have become a hot market for investors. The company said in April 2021 that it was valued at $3.8 billion after a secondary tender offering.By Chris DolmetschLearn more:How Brands Are Using NFTs to Keep Customers HookedBrands like Adidas, Gucci and The Hundreds are finding the tokens are a great way to reward their superfans. But maintaining that loyalty can be hard work.