Opera, the company that makes the cross-platform Web browser with the same name, filed an antitrust complaint against Microsoft with the European Union on Wednesday. The complaint alleges that Microsoft is engaging in anti-competitive behavior and is abusing its monopoly powers by tying its Internet Explorer Web browser to the Windows operating system.

Opera CEO Jon von Tetzchner commented "We are filing this complaint on behalf of all consumers who are tired of having a monopolist make choices for them."

The company also claimed that Microsoft is intentionally refusing to follow industry standards which hampers the ability of Web developers to create browser-compliant sites.

"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 weive brought fair and equitable options to consumers worldwide," he said.

Opera is asking the EU Commission to force Microsoft to unbundle Internet Explorer from Windows or include alternative Web browsers as part of the Windows installation. The company is also asking the Commission to require Microsoft to follow open and accepted Web standards so that site developers can code for all sites instead of having to choose between coding for Internet Explorer or most other browsers.

The complaint contends that Microsoftis unilateral control over some standards has hampered innovation and creates artificial standards that cost more to support, are more difficult to maintain, and can expose users to unnecessary security risks.

"The European Court of First Instance confirmed in September that Microsoft has illegally tied Windows Media Player to Windows," Mr. Tetzchner said. "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."

There is no word yet on when to expect a ruling from the EU Commission.