The European Club Association has slammed FIFA as world football's governing body looks to press ahead with plans to host the World Cup every two years.
The plans, which are being pushed by former Arsenal manager Arsene Wenger in his role as chief of global football development, would see the tournament played every other year with fewer international breaks during the season to make up for it.
Clubs have expressed concerns about adding to an already busy schedule though, while the plans have been unpopular with fans.
Now the ECA, which counts Celtic and Rangers as well as Aberdeen, Hearts and Motherwell among its members, has condemned the plans.
A scathing statement said: "ECA has been clear in its position that changes are needed to the IMC (international match calendar).
"A modernised and simpler IMC needs to be founded on fewer release windows; better player protection and health; and a balanced approach to club and international football. To that end, ECA has made clear – publicly, privately and repeatedly – its availability to engage with FIFA to agree what those changes should be.
"ECA has therefore followed with grave concern and alarm FIFA’s launch of active PR campaigns and much pretence, apparently seeking to railroad through reforms to the IMC, particularly the introduction of a biennial World Cup.
"Aside from the notable lack of genuine (or indeed any) consultation, and as many stakeholders have pointed out in recent days, FIFA’s proposals would lead to a direct and destructive impact on the club game, both domestically and internationally. In addition, the proposals would put players’ health and wellbeing at risk.
"They would dilute the value and meaning of club and country competitions. They would diminish and conflict with women’s and youth football – being under-represented areas of the game where ECA and others are committing significant time, talent and resources – while also subordinating other sporting tournaments and interests at all levels worldwide.
"Given the centrality of the IMC to club football, and of club football to the IMC, ECA reiterates in the most unambiguous terms that any decisions relating to its future can only come about with the consent of football clubs, with player welfare at their heart – and in keeping with legally binding obligations which ordinarily should not need re-stating.
"In short, the reform of the IMC must be founded on jointly-agreed outcomes, balanced in the interests of all, following honest and detailed consultation – not simply railroaded in the singular interests of FIFA on the back of a series of PR campaigns."