The Heineken Cup is at crisis point after England's top clubs said they were joining the elite French sides in boycotting next year's competition.
Rugby union politics is a complicated world at the best of times so BBC Sport has attempted to simplify the various strands of the interminable rows damaging the game.
What is the problem?
England's top flight clubs confirmed their decision to pull out of the Heineken Cup after their French counterparts announced their boycott on Thursday.
The French clubs were the first to announce they were pulling out of the competition back in January.
They blamed the Rugby Football Union's (RFU) refusal to hand England's top clubs, who are represented by umbrella group Premier Rugby, an equal share of the voting rights and shares in the competition.
Domestic fixture congestion in France caused by the World Cup is also seen by many as a major reason for the planned withdrawal.
England's top 12 clubs have now voted unanimously to quit the event.
The English clubs' decision has angered the RFU, which says it could take Premier Rugby to court if they go through with their threat to arrange alternative competitions.
The RFU insists Premier Rugby has a legal obligation to play in the event until 2009.
What is the RFU's position?
The RFU and Premier Rugby are engaged in a long-running battle for control of the game in England.
The RFU is reluctant to hand over equal voting rights and shares in European Cup Rugby (ERC), which runs the Heineken Cup, whereas the French and Italian authorities have agreed to do so.
The RFU appears to be using it as bargaining tool to gain greater control of England players.
England internationals are contracted by the top clubs rather than by the central union as in countries like New Zealand and Ireland.
The "Long Form Agreement", which sets out arrangements on player release between the RFU and the elite clubs, is due to expire in 2009.
The RFU wants greater control over the players and while Premier Rugby has given some ground the two sides, after a brief period where it looked as though they were edging closer to an agreement, are once again at each other's throats.
The current Heineken Cup contract, called the "Paris Accord", runs out in July 2007.
However, as England's top clubs are bound to participate in RFU-sanctioned competitions until 2009, they are effectively committed to the tournament for an extra two years beyond the current agreement.
What do the English clubs say?
The English clubs want a direct say in the running of the competition, a move the RFU has not agreed to.
Under the Long Form Agreement, the clubs are bound to participate in RFU-sanctioned competitions until 2009, but Premier Rugby believes a French withdrawal has changed the conditions of the contract.
As a result the 12 clubs voted to pull out following the French clubs' decision to withdraw.
Leicester chief executive Peter Wheeler said: "The unions and clubs of Europe have been unable to persuade the English rugby union to accept a future structure of the competition on which all parties were agreed in principle last year.
"It is vital that the clubs, who are the driving forces of the tournament, have an increased say in the development of it. It should not be used as a leverage to seek greater player release for international duty."
How significant is an English and French boycott?
When English clubs boycotted the 1998-9 Heineken Cup over more political infighting with the RFU the event survived and prospered.
But with both English and French clubs refusing to play, it would be dead in the water.
Nine of the 11 winners of the event have come from the two countries and England have supplied three of the four semi-finalists this year.
And commercially they are far and away to the two biggest markets in the event.
What happens next?
The organisers of the European Cup, the ERC, are to meet with the RFU in Dublin on 11 and 12 April to discuss their options.