Microsoft is appealing the €899 million (£710m) fine imposed on it by the European Union for failing to honour a 2004 anti-trust agreement.
Microsoft spokesman Jack Evans said that the company had filed an application with the Court of First Instance in Luxembourg to annul the European Commission (EC) decision of 27 February, which imposed the fine against Microsoft.
"We are filing this appeal in a constructive effort to seek clarity from the Court," the company said in a press statement. Microsoft is not commenting further.
The Commission could not be reached for comment Friday.
According to the Wall Street Journal, Microsoft's appeal only covers the imposition of the fine, not the underlying conduct. Since the company won't comment, it's impossible right now to know its reasons for filing an appeal.
Historically, Microsoft has resisted compliance with its EU anti-trust ruling and has been reluctant to acknowledge its guilt in the case. However, some recent moves by the company to be more open about its technology practices and to release documentation for proprietary protocols to third parties seemed to indicate it has become more willing to comply with the ruling.
Thomas Vinje, a partner specialising in competition and intellectual property at Clifford Chance in Brussels, said he finds Microsoft's legal action surprising at a time when the company is trying to repair its "strained" relationship with EU antitrust officials.
"Especially in light of its effective admission that it was seeking unreasonable fees for the information required to be disclosed by the European Commission, there really can be no doubt that Microsoft was refusing to comply with the European decision and that the Commission was correct to fine it for that refusal," he said.
Vinje added that it would be better for market competition and the industry overall if instead of initiating another court battle, Microsoft would focus its attention on complying with the EU agreement. "Only then will Microsoft - and the industry and software consumers - be able to move on from this sorry saga," he wrote.
Microsoft finally came into compliance with its EU antitrust ruling - which originally surrounded Microsoft's bundling of Windows Media Player into the Windows client OS - in late October 2007. Microsoft had fought for several years to overturn the original ruling and imposed fine of then around €497 million, but lost its appeal in September 2007.
The latest fine came less than a week after Microsoft tried to appease the commission by unveiling sweeping changes in the way it will give third parties access to technology protocols for its Windows and Office products. The plan, which Microsoft CEO Steve Ballmer hailed as a "significant change" in how the company shares information, called for publishing, on its website, documentation for APIs and communications protocols that are used by high-volume products such as Windows client and server OSes, Office and other business software.
Since February, Microsoft has published tens of thousands of pages of documentation for protocols online and made them openly available to developers. It has said it will continue on this path to promote more interoperability between its products and those of third parties.
To date, Microsoft has faced nearly $2.6 billion (€1.7 billion) in antitrust fines in the EU.