The G14 group of clubs believe they are coming under a "co-ordinated campaign" of attack, after Uefa's head of communications William Gaillard labelled the group as "a negative force in football".
Uefa will host a "round-table consultation exercise" with clubs, media members and supporters next month to look at the future of club competitions from 2009, but Gaillard has indicated the G14 will not be recognised as an official organisation at the talks.
Manchester United's chief executive David Gill, whose club is one of the G14's 18 members, revealed on Sunday that the group would like Uefa to consider a change of format for the Champions' League, with a possible switch to 17 match days from the current 13.
Gaillard said: "If clubs come up with this subject [the Champions' League schedule], we will discuss it, although it is difficult because of the international calendar. We have excellent relationships with all clubs. Things are different with the G14 because we do not recognise it as an organisation. There is no need for such a group.
"There could be a need for a group that does not try to segregate and truly represents the clubs but it doesn't do that. It is a negative force in football. We believe in the transparent organisation of football. With the support we have I'm sure we will prevail."
Fifa and Uefa have clashed with G14 on a number of issues, including compensation to clubs for players called up for national team duty.
The Belgian club Charleroi, with the backing of G14, are suing Fifa after one of their players, Abdelmajid Oulmers, returned from national team duty with Morocco in November 2004 suffering an injury that kept him out of action for more than six months.
Responding to Gaillard's comments, James Thellusson, spokesman for the G14, said: "What you are seeing is a co-ordinated 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?'
"Fifa and Uefa have failed to solve the issue of player release and insurance. 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." Details of the consultation exercise, which is due to take place some time in May, have not been released.
Meanwhile, fans from across the EU will seek more of a say in how clubs are run in the 25-member bloc when they take part in an independent review into the sport in Brussels today.
"All we want is a democratic representation for supporters," said Phil French, chief executive of British-based Supporters Direct. French added that Uefa and the EU authorities had indicated a wish that fans have a greater say in the boardroom.Reuse content