The clubs are represented on the European Club Association (ECA) board, which meets on Friday to see if it can sign off on UEFA’s plans to increase the number of Champions League matches from 125 to 225 in 2024.
The ECA’s chairman Andrea Agnelli has described the new format, where each team would play at least four extra group stage matches compared to now, as “ideal”.
UEFA’s proposals also controversially include plans which would effectively provide Europe’s most successful clubs with a safety net should they miss out on qualification via domestic performance.
However, it is understood some ECA members are still pushing for greater commercial control of the new competition before granting approval to UEFA’s plans.
An open letter to Agnelli, signed by 17 fans’ groups from 14 clubs who are represented on the ECA board, read: “We are writing to you on behalf of (fans) across the continent who you have chosen to ignore in your attempt to take over European football.
“Your plans to restructure the Champions League by increasing the number of games, introducing qualification based on past achievements, and monopolising commercial rights present a serious threat to the entire game.”