The U.S. Federal Trade Commission (FTC) sued Amazon on Monday, accusing the e-commerce giant of secretly and systematically overcharging advertisers by manipulating its advertising pricing and auction systems.

The lawsuit, joined by the attorneys general of 22 states, alleges that Amazon may have collected more than $20 billion in “hidden surcharges” from advertisers since changing its auction rules in 2019.

Filed in the U.S. District Court for the Western District of Washington, the case focuses on sponsored product, brand and display advertisements shown alongside search results on Amazon’s online marketplace.