Opera Software has accused Microsoft of stifling competition by tying its Internet Explorer web browser to Windows.
The complaint, filed with the European Commission, says Microsoft is abusing its dominant position in the desktop PC market by offering only Internet Explorer as a standard part of Windows, and hindering interoperability by not following accepted standards with IE.
Opera is asking the Commission, the executive branch of the European Union, to force Microsoft to unbundle IE from Windows, or include other browsers as a standard part of its operating system. It also wants it to require Microsoft to adhere to industry standards with its web browser.
The issue of standards is seen as important because if all web browsers do not use the same standards, website developers are likely to design their websites to work with the most widely-used browser, which is Internet Explorer. That gives people a disincentive to use other browsers.
Microsoft's spokesman in Brussels did not immediately have a comment on the lawsuit. The company has argued in the past that consumers benefit from its tight integration of IE and Windows.
Opera said it filed the complaint on behalf of all consumers who are tired of having a monopolist make choices for them.