The Super League project failed at launch 15 months ago but the company formed by the 12 rebel clubs _ now led by Real Madrid, Barcelona and Juventus _ has brought a case to the Court of Justice of the European Union in Luxembourg.
Judges from 15 of the 27 EU member states will hear arguments over two days with a majority of those national governments supporting UEFA.
The clubs will accuse UEFA of alleged abuses of market dominance with control of soccer competitions that breach European law.
UEFA's defense is that it protects the special place of sports in European society by running competitions in a pyramid structure open to all and funding the grass roots of the game.
A ruling is unlikely this year and will not affect the Super League clubs playing in UEFA competitions from September. Ten are in the Champions League groups with Manchester United and Arsenal in the second-tier Europa League.
It is the Luxembourg court's most anticipated sports decision since the so-called Bosman Ruling in 1995.
That case upended soccer's transfer system, drove up pay for top players and ultimately accelerated a wealth and competitive divide between rich clubs and the rest.
Now, some of those same clubs that built revenues and global brands playing in the Champions League want freedom from UEFA control to run their own competition like an American sports league.
Super League project
Since the 1990s, European soccer clubs used breakaway threats as leverage over UEFA to force changes to the Champions League.
That strategy secured more entries (currently four guaranteed places for each of England, Spain, Italy and Germany), prize money weighted toward them, extra games starting in 2024 and more say in overseeing UEFA competitions.
Those gains were not enough to stop 12 clubs launching the European Super League near midnight on a Sunday in April 2021. Crucially, the six English, three Italian and three Spanish clubs could not persuade Germany's Bayern Munich and Borussia Dortmund or Qatar-backed Paris Saint-Germain to join their rebellion.
It broke the European Clubs Asociation's signed working deal with UEFA, plus UEFA's legal statute that outlaws ``prohibited groupings'' of clubs in an unauthorized competition.
The Super League was to be a seasonlong, 20-team competition ``as soon as practicable'' to compete with the Champions League. It would play on midweeks with 15 teams getting permanent status as founders and five more accepted year-by-year.
The project was backed by bank JP Morgan with an initial 4 billion euros ($4.08 billion). The Champions League currently shares annual prize money of 2 billion euros ($2.04 billion) among 32 clubs.
The 12 rebels blamed the COVID-19 pandemic for economic instability and said they would create more high-quality matches to financially support themselves and the ``overall football pyramid.''
With hindsight, a better plan would have been a multi-division competition open to clubs from more countries with promotion and relegation between the tiers. A revised proposal is likely soon.
The original project collapsed within two days when the English clubs withdrew amid a fan backlash and government threats of legislation. They were quickly joined by Atletico Madrid, AC Milan and Inter Milan.
Madrid court referral
The febrile 48 hours from April 18-20 last year was also during the annual meeting of UEFA's 55 member federations, held in Montreux, Switzerland.
UEFA President Aleksander Ceferin denounced ``snakes'' and ``liars '' and wanted any club not renouncing the Super League kicked out of UEFA competitions ``as soon as possible.''
But the Spain-based Super League company got an interim ruling from commercial court No. 17 in Madrid. A judge blocked UEFA disciplinary action and asked the European court to interpret whether UEFA breached articles relating to EU competition law.
UEFA tried to remove the judge, Manuel Ruiz de Lara, alleging ``clear bias'' and disputed his court's jurisdiction.
Still, the Madrid court ensured UEFA will be in Luxembourg, after Real Madrid went on to win the Champions League, and UEFA's settlement deals with the nine repentant clubs could not be finalized.
The Court of Justice of the European Union takes referrals from national courts to ensure consistent application of EU law.
The potential consequences of the case mean it will be heard by the Grand Chamber _ a full bench of 15 judges.
After the court set an October deadline for written submissions, 16 national governments intervened to support the so-called `` European Sports Model.''
About 20 governments should take part in court on Monday afternoon. An all-day session Tuesday deals with judges' questions to the parties.
The court is soon in summer recess and its next word on the case is expected no sooner than September. The court's advocate general will give a non-binding opinion that indicates the judges' thinking but is not decisive.
A binding judgment will take several more months.
The result in Luxembourg is keenly awaited in Lausanne, Switzerland, where the International Olympic Committee is a long-time lobbyist for sports bodies' rights to run their own affairs.
A win for the Super League clubs will affect all Olympic sports, whose revenues are typically tiny compared to soccer. Some governing bodies could face existential threats from commercial operators creating rival events.
One such case is heard Monday morning by the same Grand Chamber of 15 judges.
The International Skating Union has its appeal hearing against the European Commission in a long-running antitrust case initially won by two Dutch speedskaters.
The skaters challenged the ISU over threats of life bans for wanting to compete at a commercial event in Dubai.
A key difference is speed skaters have few chances to earn money in a less wealthy sport. UEFA has not tried to ban players and the Super League clubs have revenues counted in hundreds of millions.