The Federal Trade Commission and a bipartisan coalition of 22 states sued Amazon on Monday for allegedly misleading advertisers over the past seven years by imposing “hidden surcharges.”

The complaint, filed in the Western District of Washington, where the online retailer’s main headquarters is based, alleges Amazon secretly inflated the prices that roughly 1.2 million advertising customers were required to pay for placing ads on its shopping platform. This was done through the technology company’s advertising auction process.