IBM, Nokia, Oracle, RealNetworks and Red Hat have all put their backing behind the EC's anti-trust stance against Microsoft.
The five IT giants have applied as a group to intervene against Microsoft as the company appeals the Commission's ruling "because they are very concerned about Microsoft's anti-competitive conduct," according to their representative, lawyer Thomas Vinje.
"Microsoft has been saying that the Commission stands alone and that it didn't have industry support. This demonstrates that that is untrue, that there is growing support for the Commission," Vinje said.
In March 2004, the Commission ordered Microsoft to pay 497 million euros fine, sell a version of its Windows without Windows Media Player, and allow other companies access to information needed to make their workgroup server products work smoothly with Windows. Microsoft appealed the ruling in June.
The five companies asked the European Union's Court of First Instance for leave to intervene in the appeal through an umbrella organization, the European Committee for Interoperable Systems (ECIS). Only parties that can show that the case will directly affect them may apply to intervene. The court has already granted RealNetworks leave to intervene in the appeal. Intervenors are allowed to access the court's case file and make written comments on proceedings.
After Microsoft lodged its appeal, it began settling long-standing disputes with some of the companies and organisations that had opposed it in the case, including Sun and the Computer and Communications Industry Association (CCIA).
Oracle and Red Hat are still members of the CCIA, but Nokia left when the association settled with Microsoft and withdrew from the European anti-trust case. Vinje previously represented the CCIA in the case.
ECIS asked to intervene in the case in December or January - after the usual deadline for filing such requests had passed, Vinje said. The group asked for the deadline to be waived because of the exceptional circumstances surrounding the CCIA's withdrawal from the case, and it is now up to the court to decide whether to accept the ECIS request, he said.
Parties which apply for leave to intervene after the deadline may not normally make written interventions nor access the court's case file, but they may be allowed to intervene orally at hearings, according to court spokesman Christopher Fretwell. He declined to say whether ECIS had applied for leave to intervene, saying the court can only confirm interventions when they are accepted or rejected.
Scarlet Pruitt contributed to this report.