IBM, Nokia, Oracle, RealNetworks and Red Hat have teamed up to offer assistance to the EC in its ongoing fight to put an end to Microsoft's near monopoly.
The five companies have formed a grouping known as the European Committee for Interoperable Systems (ECIS) and have offered to supply the EC with technical and legal support in order to defeat Microsoft's appeal against its conviction for antitrust breaches at the European Court of First Instance.
Although Microsoft has already been forced to make changes to its operating system by offering a version of Windows which isn't bundled with Media Player, the software giant is still fighting to have the record-breaking decision reversed.
The coalition has requested to be allowed to defend the EC's corner on the appeal, an EC spokesman told ZDNet UK sister site silicon.com, but because the ECIS missed a vital court date for filing their submission to join the appeal, they will be unable to attend the appeal at the European Court of First Instance.
However, the spokesman added the group will be considered "privileged partners" and will be invited to hearings on the case, asked to comment on and be advised of any action taken. "We are in constant discussion with the industry and welcome any feedback," he said.
An IBM spokesman said: "IBM is involved with numerous organisations that promote open standards and interoperability, including European Commission for Interoperable Systems. ECIS has a wide-ranging agenda on behalf of greater ICT interoperability, which is a goal that IBM supports because of the benefit that will accrue to all users of information and communications technology."
He added that the company had decided to become involved in the matter because "the case has raised a number of important issues" but would not be drawn on specific concerns that Big Blue has with Microsoft's business model.
The EC lost several high-tech players from its roster of supporters when Sun withdrew from the antitrust suit in April last year. Other ex-Microsoft antitrust opponents pulled out of the fray last year, including Novell, which received $536m from the Redmond behemoth, and the CCIA, which pocketed a $20m settlement.
While some powerful opposition has stacked up against the company, Microsoft does have supporters of its own, including the Association for Competitive Technology (ACT), of which Microsoft is a member. The ACT has also applied to intervene at the European Court of First Instance but on Microsoft's behalf.
A Microsoft spokeswoman said: "We are pleased with the strong level of support from European companies and software developers, a number of whom have intervened on our behalf in this process."