In its complaint, Shein alleges that Temu, owned by PDD Holdings, is "masquerading" as a legitimate online marketplace because it encourages its sellers to steal other brands' designs and then prevents them from removing products from the platform, even after they have admitted to infringement.

"Temu draws U.S. consumers into downloading and using its mobile application with promises of extremely low pricing. But Temu is not profiting from the sale of these products, which are priced so low that Temu must subsidize each sale, losing money on every transaction," the complaint said.