The chairman of the International Rugby Board, Dr Syd Millar, has attacked the Anglo-French clubs' Heineken Cup boycott as "absolutely disgraceful".
Millar hopes his intervention will help solve the dispute
In a powerfully-worded statement, Dr Millar said the clubs' "selfish" attitude would not be allowed to "dictate the course of world rugby".
He also said French clubs chief Serge Blanco was "naive" in his own role.
"It is unbelievable that one man should be allowed to bring European rugby to this state," Dr Millar said.
England's Premiership clubs joined the French National League (LNR), the umbrella organisation of the top two divisions in France, last Thursday in pulling out of next season's Heineken and European Challenge Cups.
Blanco, the LNR chairman, blamed the English Rugby Football Union's refusal to hand 50% of its shareholding and voting rights in European Rugby Cup Ltd, the tournament's organisers, to the English clubs.
But Dr Millar insists there is still time to reach a workable solution on the Heineken Cup's future, with the IRB hosting a meeting of the six affected unions following an ERC council meeting on Wednesday.
"The decision by the French and English clubs to withdraw from the European Rugby Cup has been described as regrettable, unfortunate and shameful," Millar said in his statement.
I can only assume that Serge Blanco is being very badly advised or he is being naïve
"It is more than that. It is absolutely disgraceful and selfish to destroy a tournament which has developed into a hugely successful and special annual rugby event that is vital to the well being of European rugby.
"It will have serious consequences for world rugby.
"This decision is not about fixing match schedule congestion in France as was first suggested.
"Indeed it is difficult for the average rugby supporter to understand why Serge Blanco has withdrawn the French clubs.
"The IRB made the concession of allowing the French rugby Premiership (LNR) to play matches during the Rugby World Cup to alleviate match congestion in the 2007/08 season.
"He talks now for support for the English Premiership clubs, he talks of respect.
"What respect has he shown for those who have worked hard to develop this tournament into the excellent event that it has become?
"What respect is he showing for other European rugby nations who will suffer financial hardship with a direct consequence to player employment?
"What respect is there for the players who enjoy and want to play in the tournament? What respect is there for the supporters who have enjoyed the event and travelled in their tens of thousands throughout Europe in support of their teams, therefore producing a great festival of rugby?
"What respect is he showing for the sponsors and media who have made their contribution to the tournament? None.
"What respect has he shown for the French Rugby Federation and French rugby in a year that is hugely important for the game in France as it hosts the Rugby World Cup in September and October?
"He says he has no dispute with his own national union but why is he interfering with the affairs of another union?
"It is unbelievable that one man should be allowed to bring European rugby to this state. We understand that not all clubs agree. Is there no-one among the clubs of France who has the courage to say no, we will not be part of this?
"I have always had a great respect for Serge Blanco as a player and a person.
It is not too late for the Premiership clubs to reverse their decision
"But in this instance I can only assume that he is being very badly advised or he is being naïve and has allowed himself to be used by certain people in England not just to destabilise ERC but to support a challenge to the way club rugby is governed through national unions and the International Rugby Board."
Dr Millar said the English clubs had also "sought to destroy" the Heineken Cup with their boycott in 1998/99, and was scathing about their plans to set up an alternative tournament.
"What next, a new Six Nations run by the Premiership clubs?" he added.
"The Premiership clubs in the main are owned by entrepreneurs who are not used to and do not like deferring to governing bodies such as the RFU. They do not want to have a governing body which controls the game for the good of all and not just for a handful of elite professional clubs."
Dr Millar ended his statement on a conciliatoy note, voicing his hope that the Heineken and European Challenge Cup competitions could still be saved.
"It is not too late for the Premiership clubs to reverse their decision and have the courage to do so and to show the rugby world at large that they are prepared to work within a system where their voice is heard and has been listened to."
He concluded: "The rugby unions of the world will not allow 26 clubs to dictate the course of world rugby and the present situation has brought those unions even closer and more determined to preserve the game for the good of all.
"Rugby has progressed enormously over the past few years and will continue to grow under the guidance of the unions and IRB who cater for the needs of all the game's stakeholders.
"The IRB has obligations to all of its stakeholders and envisages meetings with other senior unions around the world to allay their fears on the direction professional rugby is taking in Europe due to the actions of the English and French clubs."
Premier Rugby, the Premiership clubs umbrella body, was studying Dr Millar's statement and considering its response.
It argues the RFU has reneged on a deal struck last October over the shareholding rights, something Twickenham's top brass categorically deny.
The RFU says it would agree to the clubs' request but not in isolation - it wants it to form part of a wider-reaching domestic agreement covering international release periods and player welfare.
The knock-on effects of any boycott could be severe.
The four Welsh regions are set to lose £500,000 each while the Scottish Rugby Union warned their professional game could die without European competition next year.