Fifteen Serie A clubs oppose Champions League reforms
Juventus president Andrea Agnelli, who is also president of the ECA, last week defended plans to reform the Champions League at a UEFA congress as an attempt to save smaller clubs from "the protectionism of the big five leagues".
A vote was held on Monday by the Italian Football League concerning a joint text opposing the project, Gazzetta Dello Sport reported.
Juventus were alone in opposing the text, while Roma, Inter Milan, AC Milan and Fiorentina, abstained.
The ECA has proposed a competition made up of 128 teams in three divisions.
The top division would be made up of four groups of eight teams, with the top six in each qualifying for the following edition regardless of where they finish in their domestic leagues.
But the 15 Serie A teams opposing it believe the plans could lead to a decrease of as much as 35 percent in top-flight revenues.
The proposed reforms remain unpopular throughout European football with the Premier League, which had four teams in the finals of the Champions League and Europa League, having unanimously opposed the project.
Seven Spanish clubs, but not Real Madrid nor Barcelona, are also against the plans, along with the Bundesliga clubs, while 17 Ligue 1 sides came out against the project while Paris Saint-Germain, Lyon and Marseille abstained.