Microsoft is to appeal against the European Commission's €899m fine for failing to honour a four year-old antitrust agreement.

The move seems to bring to an end the more conciliatory approach Microsoft has recently adopted in its turbulent dealings with the Commission.

This mood has been matched in the EU, with an MP calling for a halt on Microsoft purchases until the company pays up.

The €899m fine relates to the Commission's insistence in 2004 that Microsoft license Windows code to open source developers at a reasonable price.

After a long legal tussle in the European courts, Microsoft said in October 2007 that it would comply.

The company has since demonstrated its plans for releasing Windows code to third parties, but the Commission decided that Microsoft has not done enough to comply with the ruling.

A new fine was imposed on 27 February 2008. Microsoft's appeal to the Court of First Instance in Luxembourg is to overturn the fine.