It is anticipated three more clubs will join the breakaway group as founding members with the new competition, which will begin "as soon as practicable" to eventually feature 20 teams.
After the plans emerged on Sunday afternoon, the backlash was instantaneous throughout the game and beyond, before the clubs released statements just before midnight stating their intentions.
UEFA, along with the Football Associations of England, Spain and Italy, plus the Premier League, LaLiga and Serie A, said they would use all available means to stop the "cynical project".
A joint statement, issued before the later Super League announcement, read: "If this were to happen, we wish to reiterate that we 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.
"We will consider all measures available to us, at all levels, both judicial and sporting in order to prevent this happening. Football is based on open competitions and sporting merit; it cannot be any other way.
"As previously announced by FIFA and the six federations, 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.
"We thank those clubs in other countries, especially the French and German clubs, who have refused to sign up to this. 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."
In a solo statement, the FA added the plan was "damaging to English and European football at all levels" and would "attack the principles of open competition and sporting merit which are fundamental to competitive sport". The Premier League also warned it would have a "deeply damaging impact".