Microsoft is appealing against the unprecedented fine of â‚¬899 million (US$1.4 billion) fine imposed by the European Commission in February.
The fine was in response to what the EC saw as the company's refusal to comply with its demands to stop anti-competitive business practices through its Windows operating system.
Back in 2004, the Commission ordered Microsoft to provide detailed technical information, on "reasonable terms" to rivals so that they could develop products to run on the Windows operating system. The Commission deems the royalties demanded by the software giant are unreasonable.
However, Microsoft and others are arguing that there was not a sufficiently clear definition of reasonable and that the EC's legal procedure was flawed.
According to the Financial Times, "It was widely believed in Brussels that Microsoft's desire to put the bruising decade-long battle with Europe's top antitrust regulators behind it would override issues involved in the decision about the fine itself."
At the beginning of this year the Commission launched an investigation into whether Microsoft has unfairly exploited the dominance of its Office software suite, and also whether it had illegally linked its Internet Explorer program to Windows.