The three clubs have so far refused to renounce the competition despite their nine fellow founding members withdrawing.
The trio claim it is “incomprehensible” that European governing body UEFA has begun disciplinary proceedings and warned the game faces an “inevitable downfall” without reform.
The clubs claim UEFA should not have taken any action while the matter is the subject of legal proceedings.
The clubs took the matter to a commercial court in Madrid, which referred it on to the European Court of Justice.
A statement issued on Barcelona’s website read: “FC Barcelona, Juventus FC and Real Madrid CF wish to express 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.
“Therefore, 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 toward the authority of the courts of justice themselves.”
The nine other clubs involved, including six from the Premier League, have already accepted financial sanctions from UEFA.
The statement added: “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.
“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.
“Either we reform football or we will have to watch its inevitable downfall.”
Additional reporting by PA.