In a letter to the World Leagues Association (WLA) and FIFPRO, Mattias Grafstrom, secretary general of world football's governing body, insisted they had consulted widely on the new international calendar.
"From the outset we reject any suggestion or inference that FIFA somehow "imposes" the International Match Calendar (IMC) on the football community without adequate consultation or to suit its own "business strategy"," Grafstrom said in a letter seen by AFP.
On Thursday, the leagues and unions had called on FIFA to reschedule the 32-team Club World Cup, due to be staged between June 13 and July 15 next year, or face legal action.
A letter sent by the WLA and FIFPRO, the international players' union, to FIFA president Gianni Infantino, claimed the sport's worldwide schedule is now "beyond saturation".
Grafstrom said FIFA is "like any other competition organiser" and "fully within our rights to set the parameters of our competitions whilst respecting the regulatory framework in place".
He also took aim at domestic leagues, such as the Premier League, organising summer competitions.
"We are also well aware that there are other competition organisers, including those represented by the WLA, who are similarly entitled to exercise their rights in the same manner, including the ability to introduce, abolish or replace competitions, and to review their formats in a reasonable way," he said.
"This ability has been demonstrated by the introduction of international tours by members of the WLA in recent years, by way of example.
"It would be useful for us to understand if the motivations expressed in your letter have resulted in similar written representations and references to legal action to your members or other competition organisers."
He also stressed that FIFA had consulted extensively over the 2025 to 2030 international match calendar with the WLA and FIFPRO, which was confirmed at FIFA Congress in March last year.
"Any suggestion that (FIFA) does not, or has not (consulted), is not supported by the facts," Grafstrom wrote.
Grafstrom said that calendar issues were discussed with FIFPRO and WLA "on several occasions" as part of the 'Future of Football' debate in 2021 and 2022.
The Swedish official added that while he disagreed with the "tenor and content" of the league and union letter, FIFA was keen to organise a meeting with them over the summer to discuss the issue further.