EBay, of San Jose, Calif., said the plaintiff filed the suit this month and seeks treble damages and an injunction. EBay believes it has "meritorious defenses" and intends to defend itself "vigorously," according to a filing with the Securities and Exchange Commission.

The company has come under criticism for PayPal, an online payment service that eBay owns. Last September, PayPal signed an agreement with 28 state attorneys general involving accusations of misleading business practices. It also reached a preliminary settlement agreement with a proposed class of PayPal customers.

PayPal has faced competition recently from search giant Google Inc. (GOOG), which rolled out a rival online payment service in June. Ebay said at the time that it wouldn't allow its customers to use Google's Checkout on the eBay site.