The G14 group of leading European clubs has attacked Uefa for saying that it is "a negative force in football".
G14 spokesperson James Thellusson said: "What you're seeing is a campaign to attack the G14.
"The reason for this is because we have had the temerity to ask an independent open tribunal to answer the question: 'Are Fifa and Uefa's rules legal?'"
Uefa's William Gaillard had said: "There's no need for such a group. It is a negative force in football."
Thellusson's comments relate to the story involving Belgian club Charleroi and their player Abdelmajid Oulmers.
Charleroi, with the backing of G14, are suing Fifa after Oulmers, returned from national team duty with Morocco in November 2004 suffering an injury that kept him out of action for over six months.
"Fifa and Uefa have failed to solve the issue of player release and insurance," added Thellusson.
"The key issues, which are not going to go away, are better protection for clubs against player injuries, better representation, and compensation for player release."
Meanwhile, Manchester United's chief executive David Gill, whose club is one of the 18 members of the G14, said the group would like Uefa to change the format of the Champions League from 13 match days to 17.
Uefa will hold a conference with clubs, media and supporters next month to discuss the future of club competitions from 2009.
Gaillard said Uefa was happy to talk to individual clubs about their opinions on matters regarding European competitions, but insisted the governing body does not recognise the G14.
"If clubs come up with this subject (of the Champions League match schedule), we will of course discuss it, although it is difficult because of the international calendar," said Gaillard.
"We have excellent relationships with all clubs. Things are different with the G14, because we do not recognise it as an organisation."