Barcelona, Real Madrid and Juventus have launched an attack on UEFA for opening disciplinary cases against them over their roles in trying to launch a European Super League.
The three giants said on Wednesday that they wouldn't accept being pressured by European soccer's governing body.
They also defended their attempt to remake European soccer, saying the sport is headed for an "inevitable downfall" unless there are major reforms.
The three clubs are the remaining holdouts among 12 founders of the failed Super League and have refused to renounce the project.
They released a statement on Tuesday, a day after UEFA said it had opened proceedings against them for "a potential violation of UEFA's legal framework."
Its statutes include a section on "prohibited groupings" of clubs or leagues forming without UEFA's permission or outside its control. The proceedings could lead to the clubs being banned from the Champions League.
"Barcelona, Juventus and Real Madrid, all of them more than a century old, will not accept any form of coercion or intolerable pressure, while they remain strong in their willingness to debate, respectfully and through dialogue, the urgent solutions that football currently needs," the clubs said.
"Instead of exploring ways of modernising football through open dialogue, UEFA expects us to withdraw the ongoing court proceedings that question their monopoly over European football," they said.
"Either we reform football or we will have to watch its inevitable downfall."
The three clubs expressed their "absolute rejection of the insistent coercion that UEFA has been maintaining towards three of the most relevant institutions in the history of football."
"This alarming attitude constitutes a flagrant breach of the decision of the courts of justice, which have already made a clear statement warning UEFA to refrain from taking any action that could penalise the founding clubs of the Super League while the legal proceedings are ongoing," the three clubs said.
A court in Madrid last month issued a preliminary ruling stopping UEFA, FIFA and its members from acting against the creation of the new league, which folded anyway because of widespread criticism from fans, domestic leagues and other clubs.
A judge has asked the European Court of Justice in Luxembourg to consider if restrictions on the rebel clubs are breaking European Union laws.
The holdout clubs said the opening of disciplinary proceedings by UEFA is "incomprehensible and is a direct attack against the rule of law that we, the citizens of the European Union, have democratically built up, while constituting a lack of respect towards the authority of the courts of justice themselves."
UEFA gave no timetable for the expected disciplinary cases against the clubs, who have all qualified for the Champions League next season.