English opposition to the Super League intensified on Tuesday when the Premier League threatened action against the six rebel clubs and Prime Minister Boris Johnson considered introducing laws to stop them forming the new European competition.
Divisions within the Super League clubs also grew with Manchester City manager Pep Guardiola saying joining a largely closed competition away from UEFA's existing Champions League could damage the integrity and values of sport.
Liverpool manager Jrgen Klopp has also expressed concerns about the actions of his club's owners.
The Premier League has already threatened the six Super League clubs with expulsion if they go it alone in Europe. The other 14 clubs met on Tuesday and "unanimously and vigorously" rejected the Super League plans.
"The Premier League is considering all actions available to prevent it from progressing, as well as holding those shareholders involved to account under its rules," the English top division said in a statement.
The six clubs, driven by the American owners of Manchester United, Liverpool and Arsenal, have teamed up with three elite teams from both Spain and Italy to rip up the structures of the European game.
Chelsea and Tottenham are also part of the breakaway that would see them guaranteed entry each year into the Super League rather than having to qualify through the previous season's Premier League placing.
"Sport is not a sport when the relationship between the effort and the success, the effort and reward doesn't exist," said Guardiola, whose Manchester City side leads the Premier League.
"It's not a sport. It's not a sport when success is already guaranteed. It's not a sport when it doesn't matter when you lose."
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Premier League officials were also part of a meeting alongside representatives of fan groups led from Downing Street by Johnson, who called the Super League "anti-competitive" and pledged to "drop a legislative bomb" on it if necessary.
The government could adopt the 50-plus-1 rule from Germany that gives fans the majority of voting rights, nominally to protect clubs from being controlled by private investors.
"All attendees agreed that action was necessary to protect the fairness and open competition we expect to see in football, and to uphold the fundamental principle that any club should have the chance to play and win against the biggest players in the game," Johnson's Downing Street office said in a statement.
The Super League aims for 15 founding Super League clubs, three places are yet to be filled, and only five spots with more open access.
"The Prime Minister confirmed the government will not stand by while a small handful of owners create a closed shop," Downing Street said.
"He was clear that no action is off the table and the government is exploring every possibility, including legislative options, to ensure these proposals are stopped."
Everton decried the "preposterous arrogance" of Super League clubs. Everton's nine titles are the fourth most by a team in the history of the English top division, and the club from Merseyside was considered part of the country's elite in the 1980s and early 1990s.
"The backlash is understandable and deserved and has to be listened to," Everton's board of directors said in a statement.
"This preposterous arrogance is not wanted anywhere in football outside of the clubs that have drafted this plan."
Everton's majority owner, British-Iranian businessman Farhad Moshiri, has spent heavily in recent years in an effort to push the team, which is managed by Carlo Ancelotti, into the group stage of the Champions League for the first time.
West Ham is also pursuing a top-four finish to qualify for the Champions League for the first time. The east London club said the Super League is an "attack on sporting integrity, undermines competition."