Microsoft is standing firm against the European Commission, insisting the company has fully complied with demands to open up its Windows operating systems to rivals.
The US software giant responded to a Commission ultimatum with a defiant statement accusing Brussels of ignoring the company's efforts to relax its software monopoly.
The Commission has threatened daily fines of nearly £1.4 million from Saturday unless Microsoft complies with a landmark Commission decision nearly two years ago citing abuse of a dominant market position.
The Commission ruling in March 2004 fined Microsoft nearly £350 million and ordered it to "unbundle" its Media Player software packages. Microsoft was also ordered "to disclose complete and accurate interface documentation which would allow non-Microsoft work group servers to achieve full inter-operability with Windows PCs and servers".
Two failed appeals and a final Commission deadline later, Microsoft issued a statement making clear it believed it had done everything necessary.
In particular Microsoft says its offer of thousands of pages of technical specifications enabling rivals to develop Windows-compatible software complies with the Commission's demands.
"Microsoft has complied fully with the technical documentation requirements imposed and the Commission has ignored critical evidence in its haste to attack the company's compliance," said Microsoft's formal 75-page response.
"Hundreds of Microsoft employees and contractors have worked for more than 30,000 hours to create over 12,000 pages of detailed technical documents that are available for licence.
"In addition Microsoft has offered to provide licensees with 500 hours of technical support and has made its source code, related to all the relevant technologies, available under a reference license."
Microsoft said the Commission had "disregarded evidence and denied due process" to the company.
Last December the Commission dismissed the technical documentation on offer as so complex as to be of little practical benefit to Micro-soft's rivals.
Microsoft's dossier met a crucial deadline - giving the Commission the rest of the week to study it in detail before deciding whether to trigger the massive daily fines.