UEFA called the breakaway European Super League “a textbook example of a cartel” on day one of a two-day hearing at the European Court of Justice.
The ESL launched with 12 clubs in 2021 but collapsed within 72 hours after nine withdrew amid protests from fans and opposition from governing bodies.
Barcelona, Juventus and Real Madrid have refused to renounce the ESL.
The ESL claim UEFA and Fifa had broken European Union competition law by blocking its creation.
Its lawyer Miguel Odriozola said: “For many decades, UEFA has ruled with an iron fist and beaten away any club that threatens its monopoly.
“We have taken upon ourselves to denounce the practices of UEFA.”
The issue was referred to the ECJ from a court in Madrid which ruled UEFA should not punish the three remaining clubs in the ESL.
UEFA lawyer Donald Slater told the 15-judge panel the notion of a closed league of rich clubs is “a textbook example of a cartel”.
“If UEFA had been compelled to authorise such a closed competition, other closed leagues would have emerged, leading to a systemic collapse of the European sports model,” he added.
UEFA also said there was no conflict of interest in its role as regulator and also as a commercial entity.
On the opening day in Luxembourg, submissions were also made on behalf of Fifa, La Liga and the Spanish football federation as well as from 21 EU member states and the European Commission.
The judges are expected to ask questions of the different parties involved on Tuesday when the hearing concludes.
The advocate general in the case, who is listed as Athanasios Rantos from Greece, will provide a written opinion on how he believes the court should act, but this is not expected until September prior to any ruling.
A final decision is not expected before the end of this year or even early 2023.
The nine clubs who withdrew from the ESL included six from England – Arsenal, Chelsea, Liverpool, Manchester City, Manchester United and Tottenham – plus AC Milan, Atletico Madrid and Inter Milan. (BBC)