Microsoft said on Wednesday it filed a lawsuit against the European Commission in a European Union court, the latest wrangle in its long-running battle against competition authorities in Brussels.

"Microsoft has filed an application for annulment with the Court of First Instance specifically concerning the issue of broad licences for the source code of communications protocols," a company spokesman said.

The issue relates to server software which runs printing, filing and security tasks for small office groups.

The Commission was expected to comment at its regular midday briefing.

The Commission imposed sanctions against the software giant, including a record 497 million-euro fine, in March 2004 in a case which also covered the bundling of Microsoft's Media Player with Windows, but the company has not entirely carried them out.

Microsoft challenged the Commission's decision -- a case which has yet to go to hearing -- and, separately, tried without success to get the sanctions suspended by the court.

Competition Commissioner Neelie Kroes had warned Microsoft it had to comply by June 1, 2005, or face new enforcement action.

Microsoft filed a compliance agreement by the deadline.

But it managed to soften a remedy which required it to share communications protocols -- software rules of the road -- with all rival makers of server software for small offices.

Essentially, the Commission and Microsoft agreed that those who received the protocols could not make them public.

The makers of open-source server software, who publish the source codes for all products they issue, cried foul at this, however, and Microsoft and the Commission decided to leave the issue to the Court of First Instance.

"This filing is the result of the agreement reached with the Commission in June to put this particular issue to the court for guidance and to avoid any further delay in the process," a Microsoft spokesman said of the filing.

"We are taking this step so the court can begin its review of this issue now, given its far-reaching implications for the protection of our intellectual property rights around the world," the spokesman said.