The EC (European Commission) has decided to increase the daily penalty against Microsoft for failing to honour the antitrust ruling against it from €2m (about £1.4m) to €3m (£2.1m), a source close to the EC said today.

The EC is expected to fine the software company up to €2m a day tomorrow, covering the period from 15 December last year to the present. That fine could total €400m (£277m).

The increased daily fine will be applied moving forward if Microsoft continues not to comply with the ruling, the person close to the EC said, speaking on condition of anonymity.

As part of the 2004 antitrust ruling against Microsoft, the company was ordered to reveal technical information about its Windows OS (operating system) to rival software makers. Withholding the information amounted to an abuse of the dominance of Windows, the EC ruled.

Microsoft has continually argued that the EC's demands are not clear. Last quarter it said it finally understood what it was looking for, following an oral hearing with the EC, competitors and Neil Barrett, the monitoring trustee overseeing Microsoft's compliance.

Last week it said it is working hard to meet an 18 July deadline for the final submission of the technical information. It claims the deadline was set by the EC, the monitoring trustee and Microsoft itself.

However, the EC denies it had anything to do with setting the deadline. "There was no joint setting of deadlines. There was no agreement on the timetable," the source said.

The EC will take at least two months to assess the final instalment of technical information to be submitted on 18 July. If it is deemed satisfactory, the few days between Wednesday and the final submission of the technical information will be waived and the EC will not impose the higher fine.

"The EC doesn't want to fine Microsoft again. It wants the fine for the period from 15 December to be a sufficient deterrent," the person said.

But he stressed the possible need for a greater deterrent. "The EC has no guarantee that the information submitted on 18 July will be adequate. It will have to look at it and if it isn’t enough, then the increased daily fine will be applied," he said.

Neither the EC nor Microsoft were immediately available to comment.