The bitter battle for control of the game and its lucrative revenue entered a new phase with a letter sent by the 12 clubs to UEFA on Monday in which they said they would take legal steps in unnamed courts to protect their interests as they set up the league.
The breakaway has been heavily criticised by soccer authorities, fan organisations and politicians across Europe who say it entrenches the wealth and power of a small elite of clubs.
A spokesman for the European Union's executive said there should 'solidarity from top to the bottom so that everybody gets a chance basically to take part.'
"These traditions of how people engage with sport at all levels need to be maintained as they are part of the European DNA," EU Commission spokeswoman Sonya Gospodinova said.
UEFA is ready to fight the breakaway and said on Sunday that it will "consider all measures available to us, at all levels, both judicial and sporting in order to prevent this happening".