The U.S. Federal Trade Commission has sued Amazon.com in a long-anticipated antitrust case, accusing the e-commerce giant of monopolizing online marketplace services by degrading quality for shoppers and overcharging sellers.

In a complaint filed in federal court in Seattle on Tuesday, the FTC and 17 states accused Amazon of engaging in a course of conduct to exclude rivals in online marketplace services and stifle competition. The company is also accused of illegally forcing sellers on its platform to use its logistics and delivery services in exchange for prominent placement, and of punishing merchants who offer lower prices on competing sites.

"Amazon is a monopolist and it is exploiting its monopolies in ways that leave shoppers and sellers paying more for worse service,” FTC Chair Lina Khan said in a briefing with reporters. "The stakes here are high. There is immediate harm that is ongoing. Sellers are paying $1 of every $2 to Amazon.”