After that time has passed, they will examine alternative options.
ERC stakeholders are scheduled to meet in Dublin on September 18 to begin talks over what format the competition should take when the current agreement ends in 2014.
England's clubs have threatened to form a breakaway tournament with their French counterparts unless changes to the qualification process are made.
The Aviva Premiership and Top 14 maintain that teams from the RaboDirect Pro12, who automatically enter the competition, are given an unfair advantage.
The effective deadline for a new accord to be agreed is 2014 when the existing one expires, providing a potential two-year window for the posturing and brinkmanship to continue.
However Patrick Wolff, the vice president of the French National Rugby League which runs the Top 14, has demanded a resolution within three months.
"The talks will begin on September 18 when the French clubs will ask for certain changes to the organisation and schedule of the competition," Wolff said.
"This is a platform to negotiate, it's not about exerting pressure for a boycott or forming a new competition.
"We must give negotiation a chance because the competition is more interesting with the Celts involved. We expect to find a common understanding with all the stakeholders.
"If the negotiations fail, we will see what our alternative options are.
"What's important for us is that these negotiations are completed by the end of autumn.
"This schedule is very important for us - we must have something agreed by October or November.
"If we don't we'll have to look at how the nine dates set aside for European competition can be used in other ways."
Wolff outlined the demands that will be made by the French clubs during the meeting on September 18.
"The Amlin Challenge Cup must have teams from all stakeholders because at the moment it is a useless competition just concerning English and French clubs," he said.
"We want a decent schedule to the season whereby European competition will be finished by the end of April.
"We also believe it would be interesting - even for the Celts - if the RaboDirect teams have to qualify like the English and French clubs do.
"We believe that would give more momentum to their competition.
"Our thoughts have already been transmitted to ERC and the stakeholders and will form the basis for negotiations on September 18."
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