The European Club Association (ECA) has joined critics of FIFA's controversial plans for biennial World Cups.
The ECA claimed that FIFA's plans would "lead to a direct and destructive impact on the club game" were they to go ahead.
The global governing body has proposed plans, led by former Arsenal manager Arsene Wenger, to hold a men's World Cup every two years in an overhaul of the existing international match calendar.
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FIFA's proposals have been widely criticised, including by CONMEBOL and UEFA president Aleksander Ceferin.
The influential ECA, which represents 247 clubs in the continent, suggested that "changes are needed" to football's calendar but that the planned changes were "in direct and unilateral breach of certain legal obligations."
"[The ECA has] 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," a statement from the body said.
"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 restating."
Wenger had earlier this week claimed that he was ready to "gamble" for football's future by overhauling the calendar to tackle the "chaos" and "congestion" in the game.
The Frenchman, now head of global development at FIFA, believes his proposals would improve football and has previously claimed that fans desire more high-stakes competition in international football.
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