Microsoft is facing another antitrust investigation, this time in Europe.

The European Commission has announced that it's opening proceedings against Microsoft for allegedly trying to extend its dominance of the PC operating systems business into the market for server software.

Acting on a complaint initially filed in late 1998 by Sun Microsystems, one of Microsoft's most bitter rivals, the European Commission said it sent a "statement of objections" to Microsoft charging that evidence shows the software vendor "did not carry out its obligation to disclose sufficient interface information about its PC operating system" to Sun and other server-level competitors.

The information was shared with companies "only on a partial and discriminatory basis," the commission claimed.

Mario Monti, Europe's competition commissioner, said in a statement that European officials "will not tolerate the extension of existing dominance into adjacent markets through the leveraging of market power by anticompetitive means."

In response, Microsoft was adamant that it hadn't committed any of the abuses alleged in the statement of objections. "There's no factual support for this by any customer anywhere in the world," said company spokesman Jim Cullinan. "It's a complete red herring."

Under the European Commission's rules, Microsoft has two months to reply in writing to the statement of objections.

It also can ask for a hearing, which probably would take place about a month after the written reply was submitted.

The opening of the European proceedings comes as the U.S. Supreme Court is accepting arguments in the antitrust case filed against the company by the U.S. Department of Justice (DOJ).

At issue here is whether the Supreme Court should hear Microsoft's appeal of a breakup order issued in June against the company by U.S. District Judge Thomas Penfield Jackson or send the case to the U.S. Court of Appeals in Washington for an initial review of Jackson's ruling.