Fifa’s calendar revamp would “lead to a direct and destructive impact on the club game”, says the European Club Association.
World football’s governing body has proposed a men’s World Cup every two years as part of an overhauled international match calendar (IMC).
The ECA said the planned changes were “in direct and unilateral breach of certain legal obligations”.
It also criticised Fifa for a lack of consultation about its reforms.
In an exclusive interview with BBC podcast The Sports Desk, Arsene Wenger – Fifa’s head of global development – said proposals would tackle “chaos” and “congestion” in the game.
The ECA, which represents more than 230 clubs across the continent, said that that “changes are needed” to the IMC to make it “modernised and simpler” but was unhappy with the plans and the way Fifa was going about it.
European football’s governing body Uefa has said the plans created four significant “dangers” for football, including a potential loss in prestige for the World Cup and concerns over player welfare.