The complaint follows the European Court of First Instance's backing in September of earlier European Commission antitrust penalties against the software giant.
Opera Software's complaint claims that Microsoft is acting unfairly by tying its own browser, Internet Explorer, to its dominant operating system, Windows. It also complains that Microsoft is not following web standards which promote interoperability between systems.
The complaint asks the Commission to force Microsoft to either include other browsers pre-installed on its desktop or to unbundle Explorer from the operating system, and to force it to make its technology comply with open standards so that it works with third party software.
"We are filing this complaint on behalf of all consumers who are tired of having a monopolist make choices for them," said Jon von Tetzchner, chief executive of Opera. "In addition to promoting the free choice of individual consumers, we are a champion of open web standards and cross-platform innovation. We cannot rest until we've brought fair and equitable options to consumers worldwide."
Microsoft was fined €497 million in 2004 by the European Commission for abusing its dominant position in the operating system market to freeze out rivals. In September the European Court of First Instance upheld that ruling and, later, Microsoft abandoned an appeal.
The Opera action is the first complaint filed to the European Commission, which regulates competition across the European Union, since that court decision.
Microsoft said that it did not force Internet Explorer on any customer. "It’s important to note that computer users have complete freedom of choice to use and set as default any browser they wish, including Opera, and PC manufacturers can also preinstall any browser as the default on any Windows machine they sell," said a Microsoft statement issued to OUT-LAW.COM.
"We will of course cooperate with any inquiries into these issues, but we believe the inclusion of the browser into the operating system benefits consumers, and that consumers and PC manufacturers already are free to choose any browsers they wish," it said.
One of Opera's senior lawyers said that the company wanted to force Microsoft to change. "Our complaint is necessary to get Microsoft to amend its practices," said Jason Hoida, deputy general counsel at Opera.
"The European Court of First Instance confirmed in September that Microsoft has illegally tied Windows Media Player to Windows. We are simply asking the Commission to apply these same, clear principles to the Internet Explorer tie, a tie that has even more profound effects on consumers and innovation."