The Premier League's 20 clubs say they will "vigorously defend" the domestic game against any UEFA plans to alter it.
UEFA has recently started a consultation process for what are believed to be radical changes to European club football after the current arrangements expire in 2024.
It is understood that one proposal, backed by European Clubs Association chairman and Juventus owner Andrea Agnelli, could see the current Champions League format replaced with four groups of eight teams that would play each other home and away, with qualification based on historic performance as opposed to recent domestic success.
This would effectively ring-fence the competition, and its riches, for the biggest clubs but it would also mean a lot more European games and Agnelli, and other club bosses, have made little secret of their belief that the elite should play fewer domestic games to make room in the calendar.
This would have a dramatic impact on the Premier League as it would almost certainly mean reducing the competition to 18 teams and ending the involvement of top-flight sides in the Carabao Cup.
But in a statement released after an otherwise routine Premier League shareholders' meeting in London on Friday, the clubs have firmly rejected any such change to the Champions League's format or qualification criteria.
"All clubs unanimously agreed it is inappropriate for European football bodies to create plans that would alter the structures, calendar and competitiveness of the domestic game and will work together to protect the Premier League," it said.
"In England, football plays an important role in our culture and everyday life. Millions of fans attend matches across the country, with allegiances and local rivalries often passed down through generations. We have a fantastic combination of competitive football and committed fans that we will vigorously defend.
"The structures of domestic football are determined by leagues and their respective national associations. We will now work with the FA and other leagues to ensure that European football bodies understand the importance of this, and their obligation to maintain the health and sustainability of domestic league football."
The Premier League statement came an hour after the organisation that represents 35 leagues in 28 countries, including England and Scotland, wrapped up its two-day general assembly by sending a similar message to UEFA and the top clubs.
Speaking to reporters in Lisbon, European Leagues president Lars-Christer Olsson said: "Our main objective is to safeguard and protect the domestic competitions.
"We think these are the most important competitions to the fans, much more important than any international competition."