According to a letter sent to both clubs, if they miss the deadline FIFA will issue its own ruling, which is subject to appeal.
"We can confirm that a letter was sent to the parties on behalf of the chairman of the players’ status committee. Please understand we cannot comment further at this stage," FIFA said in a statement to AFP.
Nantes appealed to the commission in February after Cardiff failed to pay 17 million euros the French club said it was owed following the transfer of Argentine striker Sala, who died on January 21 in a plane crash while travelling to join his new club.
Cardiff had earlier resolved not to pay a first instalment of €6 million of the €17 million fee agreed before the accident.