The European Union fined Microsoft $732 million for failing to respect an antitrust settlement with regulators. The European Commission accused Microsoft for breaking its promise to offer millions of users of its Windows operating system a choice of rival Web browsers.

"Such a breach is, of course, very serious, irrespective of whether it was intentional or not, and it calls for a sanction," EU competition chief Joaquín Almunia said in a statement. "I hope this decision will make companies think twice before they even think of intentionally breaching their obligations or even of neglecting their duty to ensure strict compliance."

Microsoft struck a deal with the commission in 2009 to address long-running concerns related to the way the company's Web browser was tied to its Windows personal-computer operating system, which at the time had a 90% market share in Europe.

Microsoft promised to offer users a "choice screen" until 2014 to allow them to switch to other browsers. Despite early implementation, regulators later received a complaint from a third-party and spotted that the choice had been removed from February 2011 until July 2012. Internet Explorer's market share has dropped to just under 30% from 50%, which the commission said is partly because of the introduction of the choice screen.