The Washington-based CCIA, which represents rival companies such as Oracle and AOL Time Warner, claims that Microsoft has included so many hi-tech products into XP Windows that it is impossible for other computer firms to compete.

The 260 page complaint comes at a sensitive time for the software giant, as the European Commission is already on the verge of making its decision on a four year probe into similar allegations of breaches of anti-trust law.

The Software giant has given a scathing response to the allegations. Jim Desler, a company spokesman, told the Guardian that the complaint was made up of "old arguments and allegations rehashed by a group that is cynically trying to influence the process."

Complaints will not be merged

The European Commission confirmed yesterday that it would study the new case but not merge it with its ongoing investigation. This concerns allegations that the firm deliberately made the Windows operating system incompatible with other firms servers and media products to exclude them from the market.

Microsoft has argued that the complaints have already been settled by US anti-trust authorities in a 2001 settlement with the company.

While the CCIA in private wants the European Commission to break-up Microsoft, competition lawyers said that this was unlikely and that harshest penalty would probably be changes to Windows, says the FT.

The Commission also has the option of fining a firm up to 10% of its global turnover, which would be a huge sum for a company that earns over 30 billion each year.