The top clubs of England and France have confirmed they will quit the Heineken Cup next season and start a new competition called the Rugby Champions Cup.
The English and French clubs have been threatening to break away from the Heineken Cup - organised by ERC - for some time.
The Aviva Premiership and Top 14 sides want a different structure to the competition, insisting all teams - not just the English and French - should have to qualify to play in the top European competition.
Only the top six in the English and French leagues are guaranteed a place in the Heineken Cup, whereas at least 10 RaboDirect PRO12 sides - including both Scottish, both Italian and a minimum of three each from Wales and Ireland - have a free pass into the competition.
This season, of the 12 PRO12 sides, only Newport Gwent Dragons missed out on the Heineken.
The Aviva Premiership teams and Top 14 teams say the Welsh, Scottish, Irish and Italians will all be invited to enter the new competition.
A Premiership Rugby statement said: "The competition will be based on the principles of qualification on merit, a strong competition format, equality between the leagues, higher commercial values for the teams and expansion into new European markets.
"The Top 14 and Premiership Rugby clubs have already confirmed their participation in the new competition and a joint working group has been created to prepare all necessary elements in good time for the 2014/15 season."
Premiership Rugby chief executive Mark McCafferty said they have received approaches from RaboDirect PRO12 teams expressing interest in joining the breakaway competition.
"Before we can release more details we need to know over the next few weeks
which other teams will be joining the competition," McCafferty said.
"We expect those discussions to continue over the next few weeks. Once we know the final, or close to final, numbers then we settle on the competition formats.
"Various people have approached us about the possibility of joining and we've indicated to them that we'll keep their names confidential.
"We've heard that other people want to be involved in European competitions, that's why we've left the door open and expect it to be more than an Anglo-French competition.
"Once people saw on September 10 that we would seek an alternative, interest has been expressed in at least knowing exactly what will be involved - the format, commercial and financial details as well."
It remains to be seen whether the Rugby Football Union will back the breakaway competition but McCafferty is expecting their support.
"We're asking for the RFU's support against the background that there will be no ERC competition in which we're taking part at the end of the season. We need to put in place new competitions," McCafferty said.
"We ultimately expect to have RFU support and it's in the interests of English rugby to have the teams playing in a good competition at the end of the season.
"If that scenario occurs where the RFU oppose what we're doing, we'd have to look at the reasons for opposing it."