Law firm Hagens Berman filed the lawsuit in a California federal court on Friday, alleging that Ticketmaster engaged in “unlawful and unfair business practices” that ultimately harmed live eventgoers and “unjustly enriched” Ticketmaster. In a statement, the law firm said that Ticketmaster “knowingly worked with ticket scalpers” who purchased tickets from the company and then made money on secondary sales.

At the center of the lawsuit is the allegation that scalpers who buy tickets resell them at a higher price on Ticketmaster’s services.

“When you think of ticket buyers being swindled by scalpers, you likely imagine last-minute sales outside venue doors,” Steve Berman, Hagens Berman managing partner and co-founder said in a statement. “You certainly wouldn’t assume the company selling the tickets—Ticketmaster—to be the ringleader behind massive price hikes spanning millions of tickets.”

In the lawsuit, the attorneys allege that Ticketmaster’s systems allow for scalpers to buy large quantities of tickets to live events. They then use Ticketmaster’s own TradeDesk and its resale program to sell the tickets at higher prices to those who want to go to a show. Buying and selling tickets on a secondary market is legal. But when it’s done in mass quantities, the lawsuit alleges, it runs afoul of Ticketmaster’s policies.

For its part, Ticketmaster has not yet responded to the lawsuit. The company has also not responded to a Fortune request for comment.