Microsoft on Friday lodged an appeal at a European court against the record 899 million euro (1.39 billion dollar) fine imposed on it by the EU Commission for defying a landmark anti-trust ruling.
"Microsoft today filed with the Court of First Instance an application to annul the Commission decision of February 27," the spokesman for the US software giant said in Brussels.
"We are filing this appeal in a constructive effort to seek clarity from the court," in Luxembourg, he added.
A European Commission spokesman voiced confidence that the grounds for the fine were sound.
"The Commission is confident that the decision to impose the fine is legally founded," said Jonathan Todd, spokesman for EU Competition Commissioner Neelie Kroes.
EU competition regulators imposed the record fine in February after deeming that the US software giant had defied a 2004 ruling.
The European Commission, Europe's top competition watchdog, fined Microsoft 497 million euros in March that year and ordered the company to open some key software to rivals so they could make compatible products.
In July 2006, the commission fined the company a further 280 million euros after determining that it was not respecting its original ruling.
The commission hit Microsoft with another penalty, the sum of daily fines running from June 21, 2006 to October 21, 2007, because it said Microsoft had failed to charge rivals reasonable prices for access to key information about its work-group or back-office servers in contravention of the 2004 ruling.
The 899 million euro fine is the biggest ever levelled against a single company in an EU antitrust case and brings the total penalties against Microsoft to just below 1.7 billion euros.