The European Court of First Instance has agreed to allow interventions in Microsoft's appeal of the €1.1 billion (£867mn) fine it incurred from the European Commission for breaking Europe's anti-trust laws.
The line-up of participants will be almost identical to the one during the original appeal of the 2004 anti-trust ruling itself.
Trade groups the Association of Competitive Technology (ACT) and the Computing Technology Industry Association (CompTIA) will side with Microsoft, while IBM, Oracle and Red Hat will help the Commission defend itself in the court appeal.
The Free Software Foundation Europe, the Samba Team of open-source software programmers, the Software and Information Industry Association (SIIA), the European Committee for Interoperable Systems (ECIS) will also turn up in support of the Commission, the court said in a statement.
Microsoft was fined €497 million in 2004 for abusing its dominant position in the software market to the unfair detriment of competitors. It was also ordered to change its business practices to come into line with European anti-trust law.
Microsoft failed to honour this order for three years after the 2004 ruling, employing delaying tactics despite being threatened with further fines. The Commission has since imposed additional fines on the company as a result of the delays.
Microsoft is expected to dispute the additional fines, but not the original €497 million fine, people close to the case said.
More information about the participation in the new appeal can be found in this section of the Court of Justice of the European Communities' website.