Real Madrid, Barcelona and Juventus on Saturday defended the aborted Super League project in the face of "threats" from UEFA.
The three clubs are the only ones from the original 12 yet to renounce the proposed competition that would guarantee its founding members involvement every season, instead of having to qualify.
The nine clubs who have dropped out -- Tottenham, Arsenal, Manchester City, Manchester United, Chelsea, Liverpool, Atletico Madrid, Inter Milan and AC Milan -- were on Friday given a financial penalty by UEFA for their involvement.
UEFA also said it would take "appropriate action" against the three clubs who still support the Super League project.
In response, Real, Barca and Juventus said in a joint statement "the founding clubs have suffered, and continue to suffer, unacceptable third-party pressures (and) threats."
"This is intolerable under the rule of law," they added in a joint statement.
They said the Super League had been launched "with the aim of providing solutions to the current unsustainable situation in the football industry".
The Super League was announced on April 18 but two days later it collapsed as the six Premier League clubs withdrew after angry protests from supporters pressure from the British government.
Real, Barca and Juventus argued that they and the nine clubs who withdrew "shared the same concerns... that structural reforms are indispensable to ensure our sport stays appealing and survives in the long term".
They said they were "fully aware of the diversity of reactions to Super League" and were "ready to consider the proposed approach, as necessary".
But they added: "We would be highly irresponsible if, being aware of the needs and systemic crisis in the football sector, which led us to announce the Super League, we abandoned such a mission to provide effective and sustainable answers to the existential questions that threaten the football industry."
The nine clubs who abandoned the project on Friday agreed to forego five percent of their revenue from UEFA competitions for one season and between them make a 15-million-euro ($18.25 million) donation to support grassroots and youth football in Europe.
They committed to taking "all steps within their power" to end their involvement in the breakaway league and agreed to participate in UEFA competitions for which they qualify. They also agreed to pay fines of 100 million euros if they ever seek to play in an "unauthorised" competition.
Real, Barcelona and Juventus said: "We regret to see that our friends and founding partners of the Super League project have now found themselves in such an inconsistent and contradictory position when signing a number of commitments to UEFA yesterday."
The fallout from the Super League's collapse last week led to Manchester United supporters bursting into Old Trafford to stage a protest against the club's American owners, the Glazer family. The protest led to the postponement of United's Premier League match against Liverpool.