The South American football confederation (CONMEBOL) says a biennial World Cup would diminish the competition's standing.
They're against proposals to play the World Cup every two years.
In May, 166 FIFA delegates voted in favour of a feasibility study (with 22 opposed) looking into making the tournament a biennial event.
That feasibility study has effectively become a PR campaign, headed by FIFA president Gianni Infantino.
He believes urgent change is required, with "too many meaningless matches" in the international calendar.
Infantino's been backed up by FIFA's head of international development, Arsene Wenger, and a plethora of former players who form part of the FIFA 'Legends' program.
However, CONMEBOL has joined their European counterpart UEFA in speaking out against the proposal.
In a statement on Friday, they said, "A World Cup every two years could distort the most important football competition on the planet, lowering its quality and undermining its exclusive character and its current demanding standards."
They added, "A World Cup every two years would represent an overload that is practically impossible to manage in the international competition calendar.
"Under current conditions, it is already complex to harmonise times, schedules, logistics, adequate preparation of equipment and commitments.
"The situation would be extremely difficult with the proposed change. It could even put the quality of other tournaments, both club and national, at risk."
Earlier this week, UEFA president Aleksander Ceferin claimed a World Cup every two years would destroy the sport.
"I hope they [FIFA] will come to their senses, because I don’t see the right approach to go everywhere except the confederations, not to speak to us,” he told The Times.
“They didn’t come, they didn’t call, I didn’t get a letter or anything. I just read in the media.
"To play every summer a one-month tournament, for the players it’s a killer.
"If it’s every two years it clashes with the Women’s World Cup, with the Olympic football tournament.
“The value is precisely because it is every four years, you wait for it, it’s like the Olympic Games, it’s a huge event. I don’t see our federations supporting that.”
As recently as 2018, CONMEBOL president Alejandro Domínguez requested that the World Cup be played every two years.
However, they've had a change of heart - perhaps brought about by a memorandum of understanding signed in 2020, which would see CONMEBOL and UEFA align more closely to "foster the development and growth of football on both continents".
Now, the South American confederation believes a biennial World Cup is "highly unviable".