The Spanish football league, La Liga, on Friday said it had appealed to the Court of Arbitration for Sport over FIFA's decision to extend the South American (CONMEBOL) World Cup qualifying window.
World soccer's governing body announced earlier this month that fixtures missed in March due to the COVID-19 pandemic would be played in September and October, and increased the CONMEBOL international window by two days until Sept. 10.
It cited extensive travel and player safety as the reasons for the extension.
Real Madrid, Barcelona, Sevilla and Atletico Madrid are all due to play league fixtures just 24 hours later, and on Thursday LaLiga said it had held a meeting with all concerned teams, who agreed not to release their players for international duty.
The decision to seek legal backing comes just two days after FIFA president Gianni Infantino called on LaLiga and the Premier League to "show solidarity" and "preserve and protect sporting integrity" after clubs from both leagues said they would not allow players to travel to South America.
"LaLiga has today submitted an appeal and requested precautionary/interim measures before CAS against the decision of the Bureau of the FIFA Council... which infringes FIFA's own statutes and regulations," a LaLiga statement read.
"LaLiga will also file a lawsuit against FIFA in the Swiss courts for infraction of competition rules.
"LaLiga presents this case before CAS in order to defend the integrity of its competition and the rights of its clubs affected by players being called up for international duty during the upcoming CONMEBOL international match calendar ... which has been extended by two days.
"Other confederations such as UEFA and CONCACAF have not extended their match calendar despite scheduling the same number of matches (three), working to fit in three international rounds of fixtures in a maximum of ten days so as not to disrupt domestic league competitions."