MICROSOFT last night stepped up its antitrust battle with the European Commission by publishing letters between Steve Ballmer, its chief executive, and Neelie Kroes, the EU Competition Commissioner, to show that it had complied with a Brussels mandate to allow competitors access to its technology.

The letters relate to a 2004 order that the American software company allow access to its so-called group server operating system software to competitors. In December Mrs Kroes accused Microsoft of failing to comply with the order and it faces the prospect of fines of €2 million (£1.4 million) a day.

Microsoft said last night that it had decided to publish the letters on the internet to show that it had made every effort to comply with its ruling. “Transparency is vitally important in what can be a very opaque process in Brussels. We have decided to open this up so people can understand the issues,” said Horacio Gutierrez, a lawyer for Microsoft.

In a letter to Mr Ballmer dated November 9 last year, Mrs Kroes said that she was not satisfied with the speed of Microsoft’s compliance with the order but was encouraged by the actions it had taken. “I have been somewhat disappointed by the pace at which issues of compliance have been solved so far . . . I however take note of your unambiguously stated commitment to comply fully with the March 2004 decision,” she wrote.

In a reply written on December 15 — only six days before the Commission threatened to fine Microsoft €2 million a day for alleged non-compliance with the order — Mr Ballmer assured Mrs Kroes of the company’s efforts to meet and go beyond the Commission’s demands. He wrote that technical documents requested by the EU had been provided partly on paper and partly on CD. He also asked Mrs Kroes to let him know whether she needed help to access the documents on CD.

Microsoft said that Mrs Kroes and her colleagues did not bother to read the submissions before ordering the company to attend a closed-door hearing, at which it will be decided whether or not the hefty fine will be imposed on the company.

In 2004 Microsoft was found guilty of breaching European anti-trust rules by denying its competitors access to the secret source code that would enable their programmes to interact with Windows, the company’s ubiquitous computer operating system.

The company was fined €497 million and ordered to help makers of rival server operating systems to connect with servers using Windows by giving up some of its trade secrets and by providing technical assistance documents. Microsoft appealed the decision and the case will be heard in Luxembourg in two months’ time.

A spokesman for the EU said last night that the documents submitted by Microsoft in December were being read.

Jonathan Todd, a spokesman for the European Commission said: “We are carefully analysing (Microsoft’s) reply and after they have had the opportunity to present their arguments at the oral hearing we will decide whether or not to impose a daily fine.”

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