A long-running dispute between Microsoft and the European Union is set to be decided on Monday.
Microsoft's market dominance alarms regulators
The software giant will learn at about 0830BST if it has succeeded in a legal challenge to an EU ruling that it had abused its dominant market position.
A probe concluded in 2004 that Microsoft was guilty of freezing out rivals in server software and products such as media players.
It was ordered to change its business and fined 497m euros (£343m; $690m).
The 2004 ruling ordered Microsoft to ensure its products could operate with other computer systems by sharing information with rival software companies.
It was also ordered to make a version of its Windows operating system available without software such as Media Player.
Last year, Microsoft was told to pay daily fines adding up to 280.5 million euros over a six-month period, after it failed to adhere to the 2004 decision.
Threat to model
Microsoft is challenging the EU ruling, and also argues that its fine should be rescinded.
Analysts say that the landmark ruling, due from Europe's Court of First Instance, will determine how companies which have dominance in their markets should behave towards rivals.
The Commission says that, by making its own servers interoperate with desktop PCs better than those of its rivals, Microsoft drove others from the marketplace.
If the court upholds the EU's decision, analysts say that the Commission may take further cases against Microsoft and perhaps even other technology groups which hold a dominant position in their markets.
It could also damage the future business model of Microsoft.
The US firm says that such a decision would be a blow for innovative companies.
"While there are some companies who will use the press and government processes to advance their interests and invoke their view of competition law, I think we are working quite well with most firms," said Dave Heiner, Microsoft deputy general counsel who leads the company's compliance efforts.
However if the court finds in Microsoft's favour, the Commission will face having to repay fines - as well as a severe blow to its reputation.
It is also possible that the court will partly support the 2004 ruling.