UEFA is working with the European Club Association (ECA), whose members include all of the continent's biggest clubs, to redesign European competition from 2024, but the Swiss league (SFL) said their plans would have "unacceptable consequences."
Other leagues such as the Premier League, La Liga and the Bundesliga have also opposed the proposal.
The ECA is due to hold a meeting in Malta next week to discuss the proposal.
UEFA has said talks are still at a preliminary stage but representatives from several European leagues who were present at a meeting with European soccer's governing body this month said they were presented with a concrete proposal.
This involved allowing the top 24 teams in a 32-team Champions League to keep their places for the next season, ending the tradition that qualifying for European competition is achieved via national leagues.
Only four places would be open to the winners of Europe's 54 national leagues.
"The dream of participating in UEFA club competitions and the prospect of playing matches against the continent’s major traditional clubs must continue to live on," said the Swiss league's chief executive Claudius Schaeffer.
"Should this dream die, an important element of club football and supporting a team will also die.
"FC Basel 1893 against Liverpool, Young Boys playing Juventus, FC Zurich paired against AC Milan or FC Thun versus Arsenal: It’s epic games like these that create the unique excitement for European club football amongst Swiss fans," he said referring to matches that have taken place in the past.
"We want to keep the opportunity to be part of memorable European nights in the future."
(Writing by Brian Homewood; Editing by Ken Ferris)
