Arsenal, Chelsea, Liverpool, Manchester City, Manchester United and Tottenham are among 12 clubs who have agreed to join a new European Super League (ESL).
The six Premier League clubs will be joined by AC Milan, Atletico Madrid, Barcelona, Inter Milan, Juventus and Real Madrid.
The ESL said the founding clubs had agreed to establish a "new midweek competition" with teams continuing to "compete in their respective national leagues".
The new format has been put forward as a rival to the UEFA Champions League, not as a replacement to domestic leagues, but there are fears it could have wider ramifications.
It said the inaugural season was "intended to commence as soon as practicable" and "anticipated that a further three clubs" would join the breakaway.
The ESL said it also planned to launch a women's competition as soon as possible after the men's tournament starts.
UK Prime Minister Boris Johnson, Uefa and the Premier League condemned the move when the news broke on Sunday.
Mr Johnson,on Monday said the government was "going to look at everything that we can do with the football authorities to make sure that this doesn't go ahead in the way that it's currently being proposed".
Speaking to broadcasters on a visit to Gloucestershire, he said: "I don't think that it is good news for fans, I don't think it's good news for football in this country."
The 14 Premier League clubs not signed up to the ESL will meet on Tuesday to assess the proposals and consider a response.
UEFA, in a joint statement with FA, Premier League, La Liga, and Serie A, blasted the plans and did not rule out taking legal action over the proposals, insisting players involved would be banned from all other competitions at domestic, European or world level and could be prevented from representing their national teams.
FIFA and the European Club Association (ECA) have also criticised the creation of a breakaway competition.
World governing body Fifa had previously said it would not recognise such a competition, and any players involved could be denied the chance to play at a World Cup.
After the ESL was announced, Fifa expressed its "disapproval" of the proposed competition and called on "all parties involved in heated discussions to engage in calm, constructive and balanced dialogue for the good of the game".
The ESL has sent a letter to Fifa president Gianni Infantino and Uefa boss Aleksander Ceferin issuing notice of legal proceedings in European courts designed to block any sanctions the two governing bodies may try enforce over the formation of the ESL.
In a statement, the ESL said: "Going forward, the founding clubs look forward to holding discussions with Uefa and Fifa to work together in partnership to deliver the best outcomes for the new league and for football as a whole."
The league will have 20 teams - the 12 founding members plus the three unnamed clubs they expect to join soon, and five sides who qualify annually according to their domestic achievements.
Under the proposals, the ESL campaign would start in August each year, with midweek fixtures, and the clubs would be split into two groups of 10, playing each other home and away.
The top three in each group would qualify for the quarter-finals, with the teams in fourth and fifth playing a two-legged play-off for the two remaining spots.