Football's governing body had originally intended to have 16 groups of three teams after expanding from 32 to 48 nations for the tournament jointly hosted by the United States, Canada and Mexico.
However, following the Qatar 2022 edition, plans to maintain the current four-team system resurfaced and have now been rubber-stamped at FIFA's annual congress.
The decision has enraged LaLiga however, with the competition set to expand to 104 games from 64.
LaLiga has also objected to plans for a new international club tournament, which will join an expanded Club World Cup on the football calendar. The latter is due to take place every four years starting from 2025, but an as-yet-unnamed additional event is set to take place annually alongside it.
"Following the announcements made today at the 73rd FIFA Congress in Kigali, Rwanda, LaLiga states that FIFA continues its malpractice of making unilateral decisions on the world football calendar," read a statement.
"[FIFA is] showing complete disregard for the importance of national championships, and the football community in general. FIFA completely neglects the economic damage these decisions inflict on leagues around the world.
"Leagues were not consulted about any of the changes presented, especially about the new annual club competition, of which we were completely unaware, and which seriously affects our competitions.
"These decisions do not take into account the competitive, sporting and economic impact on national leagues, clubs and players, by further cramming an already overloaded schedule.
"LaLiga and other leagues represented in the World Leagues Forum will analyse FIFA's decisions and decide on the most appropriate next steps."
Under the three-team World Cup group structure, all nations would have played two games before the top pair from each group would have proceeded to a round-of-32.
Now however, the eight best-ranked third-place sides from 12 groups will also be included in the mix, with the revised format ensuring every side plays at least three games.
It also means those who reach the final will play eight games, including the showpiece match itself, one more than teams who reach the end of the tournament currently partake in.