An anonymous reader quotes a report from The Wall Street Journal: Amazon faces a formal European Union antitrust investigation (Warning: source paywalled; alternative source) into its dealings with merchants that sell goods on its site, marking an expansion of a multi-pronged regulatory push that has ensnared other U.S. tech giants like Facebook and Google. The European Commission, the EU’s top antitrust enforcer, said Wednesday that its investigation will examine whether Amazon is abusing its dual role as a marketplace where independent sellers can offer products and as a retailer of products in its own right. In particular, the probe will study whether Amazon is using nonpublic data from independent merchants to compete unfairly against them. Investigators will also examine what data Amazon uses to pick a seller as the default option for a given product when a user clicks the “buy” button — and whether Amazon has an unfair advantage to be designated the default for products it sells. The probe could eventually lead to formal charges, fines and orders for the company to change business practices, but it could also be dropped.