The European Union's executive branch has launched an antitrust investigation into online retailer Amazon over its distribution of e-books, which have become increasingly popular in recent years. The European Commission said yesterday it will investigate certain clauses in Amazon's contracts with publishers, including a requirement for publishers to inform the company about arrangements it has with Amazon competitors. Amazon is the largest distributor of e-books in Europe and owns the popular e-book device, the Kindle. Margrethe Vestager, the Commission's top official on competition policy, stressed that the investigation does not call into question Amazon's successful and comprehensive service. If the Commission finds that Amazon's arrangements limit competition and reduce consumer choice, then it could be violating antitrust rules in Europe that prohibit companies from abusing their dominant market position. The firm could be fined or forced to change its business practices. The investigation will center on English and German e-books, which are the largest markets across Europe.