A group of Microsoft rivals and customers yesterday filed a new complaint with the European Commission on Wednesday, accusing Bill Gates's US software giant of competing unfairly.
The European Committee for Interoperable Systems (ECIS) said in a statement that Microsoft "threatens to deny enterprises and individual consumers real choice".
ECIS, which dates back to 1989, includes IBM, Oracle, Sun Microsystems, Nokia, RealNetworks and others.
The complaint asks the Commission to put an end to the practices that the group says have hemmed in its members.
The group said that limits which were placed on Micro-soft in a 2004 antitrust decision - now under appeal by the company - needed to be rapidly and fully enforced.
The group said Microsoft Office software was one example of a Microsoft product that did not permit rivals to interoperate properly with the Windows operating system, preventing them from competing.
"It prevents them from achieving full interoperability," said Thomas Vinje, a lawyer for the group.
The European Commission said it had received the complaint.
Microsoft is already embroiled in a standoff with the European Commission on whether or not the group is complying with a March 2004 anti-trust decision against it, in which the software company was fined a record 497 million (£340 million) for abuse of its market position.
Microsoft yesterday shrugged off the new complaint.
"We have come to expect that as we introduce new products that benefit consumers, particularly with the kind of breakthrough technologies in Office 12 and Windows Vista, a few competitors will complain," it said.