On Sunday, a dozen of the continent’s biggest clubs from England, Spain, and Italy—including Real Madrid, Manchester United, and Juventus Turin—revealed plans to form a breakaway rival to the Champions League, the pinnacle of the European football season.

FC Barcelona, Liverpool, AC Milan, Arsenal, Atlético Madrid, Chelsea, Inter Milan, Manchester City, and Tottenham Hotspur form the remaining founding members of the proposed breakaway faction. They hope to persuade three more top-flight European teams to join their ranks in order to compete against each other as soon as possible.

The deal could cost current sponsors such as Mastercard, Heineken, and Nissan a fortune, as their investment in the Champions League would be severely damaged should such fan favorites depart en masse in favor of a new format. 

Europe’s governing body, UEFA, shot back in a statement on Monday, denouncing the plans and pledging to ban the 12 from participating in fixtures and extending this to players called up to play for their national teams. 

“All our member associations will remain united in our efforts to stop this cynical project,” UEFA said, explicitly thanking French and German clubs for refusing to follow the narrow “self-interest of a few clubs.”

The Super League also raised the ire of U.K. Prime Minister Boris Johnson, who warned the clubs “must answer to their fans” before taking any further steps.

“Plans for a European Super League would be very damaging for football,” he tweeted. “They would strike at the heart of the domestic game.”

The rebel clubs justified the plans by citing the economic effects of the COVID-19 outbreak. Some of their costs have stayed the same even as the loss of cash-paying spectators damaged revenue. After all, the clubs had to continue coughing up for the expensive stars on their roster such as Barcelona’s Lionel Messi and Cristiano Ronaldo of Juventus.

“The pandemic has laid bare the long-standing weaknesses, like the arms race for talent, and exposed the underlying unsustainability of European football,” a source at one of the founding clubs told Fortune. “Economic governance models like Financial Fair Play have failed to rein in runaway spending,” the person added.

Under the proposed plan, clubs would have to meet minimum profitability targets to ensure they don’t pile on mountains of debt to buy star players, according to the source.

The chief executive of Germany’s popular Borussia Dortmund (BVB), Hans-Joachim Watzke, said that consensus was reached at the European Club Association on Sunday evening to oppose the project.

“The ECA board members took a clear stance in rejecting plans for the establishment of a Super League,” he said in a statement posted on BVB’s website. He stressed that both German clubs on the ECA board, FC Bayern Munich and Borussia Dortmund, “shared exactly the same stance throughout all discussions.”  

Both Bundesliga clubs are majority owned by their fans, which insiders believe is a clear reason why they did not, at least initially, sign up for the proposal.  

The development comes at a delicate time, as the Premier League is set to auction the rights later this year to broadcast the 2022–25 seasons, with a number of big-name streaming platforms in the U.K. and U.S. reportedly lining up, including Amazon and Sky.

Speculation has swirled in recent years over the formation of a higher tier tournament, in part because the bloated size of the Champions League ensures a number of entirely forgettable fixtures among Europe’s footballing minnows.

The proposed Super League would include only 20 clubs, five of which would qualify on merit under current, as yet unfinalized, plans. 

The 12, which each stand to receive 3.5 billion euros, argued their combined market power ensures a much more lucrative overall pot that could be shared among their less fortunate brethren.  

Smaller clubs would receive “substantially higher” so-called solidarity payments than what they currently receive, potentially in excess of 10 billion euros during the course of the initial commitment period, they estimated.

The 12 argued the new Super League could also elevate the status of women’s club football, as a corresponding female competition would be created as soon as possible.  

“We will help football at every level and take it to its rightful place in the world. Football is the only global sport in the world with more than 4 billion fans,” Florentino Pérez, Real Madrid president and proposed Super League chairman, said in a statement on the club’s website.

Perez is also CEO of Spanish construction giant ACS.

U.S. banking giant JPMorgan confirmed it is providing upfront financing for Pérez’s project.

Speaking by phone, Ronan Evain, executive director of Football Supporters Europe, warned that a Super League that concentrated power among an elite number of clubs would be a financial catastrophe for the broader sport. 

“Football has failed to address the generational gap, with interest among youth even in Italy dropping at an incredibly fast rate. In England the average match-going fan is in his fifties and sixties since younger people cannot afford it. It’s a demographic time bomb, and this could be the final nail in the coffin,” Evain told Fortune. “It will be interesting to see how the sponsors react to this in the coming days. I still think it will fail, but it’s a serious threat.”  

Heineken and Mastercard were not reachable for a statement, while Adidas and Nissan declined to comment.

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