Microsoft and European Union regulators will square off in the EU's second highest court Monday over a fine of nearly half a billion euros that the bloc imposed on the software giant seven years ago.
Microsoft, which is refusing to pay the fine, has requested the five-day trial at the Luxembourg-based European Court of First Instance in hope of getting the penalty annulled or at least reduced.
The European Commission - the EU's executive arm - slapped a fine of 497 million euros (612 million dollars) on Microsoft in March 2004 for abusing its dominant market position.
The European competition watchdog also ordered Microsoft to sell a version of its widely-used Windows operating system unbundled from its Media Player software and to divulge information on its operating system needed by makers of rival products.
The company has spared no effort to mobilise an army of lawyers, computer experts and advisors in hope of convincing the 13 judges hearing the case that the fine is unjustified.
The Commission remains confident its anti-trust ruling is firmly grounded.
After years of failure to resolve the dispute, both sides have huge stakes riding on the judges' decision, which is not expected until the end of this year at the very earliest.
For Microsoft, a defeat would not only mean that the company cannot wiggle out of the fine but would also seriously compromise its long-standing claim that its business practices do not thwart competition.
If the Commission were to lose the case, its authority as Europe's top competition regulator would be seriously undermined.
Microsoft is eager to present the case as more than just getting the fine reduced.
"At issue are whether companies can improve their products by developing new features and whether a successful company must hand over its valuable intellectual property to competitors," Microsoft said in a statement ahead of the trial.
"There is healthy competition and interoperability in all the markets covered in this case and we will bring those facts to the court next week," it added.
But European Competition Commissioner Neelie Kroes refuses to be intimidated. On Saturday she said she was "confident" that the EU would prevail because it had "good arguments".