World players' union FIFPRO says an overhaul of the international calendar to include a World Cup every two years will not have legitimacy without the support of current male and female players.
The union says it will meet with FIFA to discuss its proposals. FIFA says its plans protect player welfare and provide more meaningful competition to players at all levels.
The shortening of the gap between World Cups has been by far the most controversial element of the plan put forward by FIFA's head of global development Arsene Wenger, the former Arsenal manager.
UEFA's member associations met on Tuesday to discuss the calendar proposals, with its president Aleksander Ceferin having already told The Times his confederation could boycott the World Cup if the changes are voted through.
FIFPRO general secretary Jonas Baer-Hoffmann said the public spat between FIFA and UEFA on this subject showed the sport's leaders had "reverted to the same old habits of conflict".
FIFPRO's statement said: "Without the agreement of the players, who bring all competitions to life on the pitch, no such reforms will have the required legitimacy.
"The current debate once again follows a flawed process and approach in which additions to the calendar are debated in public in the absence of in-depth impact assessments, transparent information, and most importantly a commitment to agree improvements for the game in good faith between all
stakeholders."
Baer-Hoffmann added: "The lack of genuine dialogue and trust between institutions in football blocks the game's ability to build more resilience after a painful pandemic, but rather we keep reverting to the same old habits of conflict."
He also said it was "frustrating" that the impact of changes to the men's calendar treated the women's game as "a side-product".
FIFA's proposals would involve the Women's World Cup sharing a summer with a men's finals, but it is understood it is looking at a July or August slot for the women's showpiece to avoid a clash.
Former United States coach Jill Ellis is leading a consultation on the international women's calendar.
FIFPRO said it could not endorse any individual reforms without "an overarching review of the men's and women's calendar" and called for any expansion of the international calendar must include proper safeguards for the health and well-being of players.
FIFA has proposed a mandatory 25-day rest period for players from the point their team is eliminated from a finals, and says its proposals do not increase the overall volume of matches because the qualification process would be simplified and shortened.
It also says cutting the number of in-season international breaks to one or a maximum of two would significantly reduce travelling for players.
Despite those pledges, there has been firm and unanimous opposition to the plans from European Leagues, an umbrella organisation which includes the Premier League and EFL among its membership. The group said it would "work together to prevent football governing bodies taking unilateral decisions that will harm domestic football".
FIFA president Gianni Infantino says he hopes a decision will be taken by the body's 211 member associations before the end of the year.
The Asian Football Confederation has not given a firm view on the detail of the plans, but released a statement on Tuesday welcoming FIFA's "consultative approach" and that it "recognises the natural synergies of organising more meaningful matches", one of the stated aims of Wenger's proposals.
