UEFA and English, Spanish and Italian football authorities announced on Sunday that any clubs who take part in a so-called European Super League would be banned from all other domestic and continental competitions as the breakaway organisers were condemned as "cynical" and "greedy".
European football's governing body said it had learned that some English, Spanish and Italian clubs might announce a breakaway competition.
"The clubs concerned will be banned from playing in any other competition at domestic, European or world level, and their players could be denied the opportunity to represent their national teams," UEFA said in a statement.
UEFA is planning to announce its own reforms to the Champions League on Monday, with an expansion to 36 teams from 32 and two 'wildcard' slots expected to be among the plans.
There would be a minimum of 10 games for each team.
Media reports on Sunday suggested that an announcement on plans to create a Super League could be made later in the day.
British media reported that Liverpool, Manchester United, Arsenal, Chelsea, Manchester City and Tottenham were the six Premier League teams set to be part of the plans.
It was widely reported that Real Madrid, Barcelona, Atletico Madrid, Juventus, Inter Milan and AC Milan make up the 12 clubs threatening the breakaway.
"If this were to happen, we wish to reiterate that we - UEFA, the English FA, RFEF, FIGC, the Premier League, La Liga, Lega Serie A, but also FIFA and all our member associations - will remain united in our efforts to stop this cynical project, a project that is founded on the self-interest of a few clubs at a time when society needs solidarity more than ever," read the statement.
Arsenal currently sit ninth in the Premier League, well off the pace in the race to qualify for Europe, while Liverpool and Chelsea are both also currently outside the Champions League spots.
"Fans of any club in England and across Europe can currently dream that their team may climb to the top and play against the best," the Premier League said in a statement.
"We believe that the concept of a European Super League would destroy this dream."
There have been no reports that French or German clubs would be part of the Super League.
"We thank those clubs in other countries, especially the French and German clubs, who have refused to sign up to this," UEFA added.
"We call on all lovers of football, supporters and politicians, to join us in fighting against such a project if it were to be announced.
"This persistent self-interest of a few has been going on for too long. Enough is enough."
Juventus are facing a battle to finish in the Serie A top four this season and seven-time European champions AC Milan have not played in the Champions League since 2014.
"It is illegitimate, irresponsible and anti-competitive by design," said Fans Europe, a football supporters' network.
"More to the point, it is driven exclusively by greed, the only ones who to stand to gain are hedge funds, oligarchs, and a handful of already wealthy clubs, many of which perform poorly in their own domestic leagues despite their inbuilt advantage."
Former Barca president Josep Maria Bartomeu, when he resigned from the role last October, said he had accepted a proposal for the Catalan giants to play in the Super League.
"Finally the 'gurus' of the superleague PowerPoint are exiting the darkness of the bar at 5AM, intoxicated with selfishness and a lack of solidarity," said La Liga president Javier Tebas on Sunday.
Notably, last season's two Champions League finalists, Bayern Munich and Paris Saint-Germain, are among the big European teams not involved.
"It would be irresponsible to irreparably damage the national leagues, as the basis of European professional football, in this way," German Football League boss Christian Seifert said.
Political leaders also slammed the clubs involved, with UK Prime Minister Boris Johnson saying they have to "answer to their fans".
"Plans for a European Super League would be very damaging for football and we support football authorities in taking action," Johnson said.
"They would strike at the heart of the domestic game, and will concern fans across the country.
"The clubs involved must answer to their fans and the wider footballing community before taking any further steps."
French President Emmanuel Macron also criticised the plans.
"The President of the Republic welcomes the position of French clubs to refuse to participate in a European football Super League project threatening the principle of solidarity and sporting merit," the Elysees Palace told AFP.