Microsoft has written to the European Commission to complain that the company is being denied the normal rights to defence in its antitrust case. In a letter sent to the Commission on Monday, a Microsoft lawyer said that the Commission was "seriously prejudicing Microsoft's rights of defence" in the ongoing antitrust case by denying the company access to certain files relating to the case.

The company argues that unless it gets access to these documents it will not to be able to meet the Commission's Feb 15 deadline to prove it is complying with its 2004 antitrust ruling. The Commission has threatened to fine the company €2 million (US$2.4 million) a day until Microsoft complies.

But the five-page letter, written by Ian Forrester QC, one of Microsoft's top lawyers, says that the earliest the company could draw up its response to the Commission is Feb 28. Commenting on the Commission's decision to extend the deadline for compliance only until Feb 15, it says that the decision seems to be based on the "fallacious notion" that extending the delay further would "cause a danger to effective competition".

Microsoft's rivals in the case say that the longer the delay in forcing the company to comply with the ruling the greater the risk that it completely consolidates its dominant position in the market.

The complaints centre on a number of files that are correspondence between the Commission, its external group of technical experts and the independent monitoring trustee who is assessing whether Microsoft is complying with the Commission's ruling.

The Commission argues that it has no obligation to release the documents Microsoft is asking for because it has granted access to the final reports by the technical experts and the monitoring trustee.

But Microsoft says that access to the files is essential to ensure it knows all the arguments being used by the Commission to say that the company has not yet complied.

The Commission has responded to the letter, saying that the "issue of Microsoft's access to documents is still the subject of continuing correspondence between the hearing officer and Microsoft", according to Jonathan Todd, spokesman for European Union Competition Commissioner Neelie Kroes. It was therefore "premature" for the company to claim that the Commission had prejudiced its right of defense.

A spokesman for Microsoft said: "All we are asking for is access to our file. This is a basic question of fairness and transparency."