The FIA has defended its "extensive and thorough investigations" into the engine Ferrari raced with last season, insisting it was "impossible" to provide evidence of a breach.
On Wednesday, seven of Formula One's 10 teams published a joint statement expressing surprise and shock at the FIA's confidential agreement with Ferrari.
The teams – including Mercedes, Red Bull and McLaren – are concerned that the FIA's investigation does not establish whether Ferrari, who finished second in the 2019 constructors' championship – bent the rules.
The FIA, however, maintain while "not fully satisfied" with Ferrari's responses, reaching the agreement was in the best interests of F1 as to "avoid the negative consequences that a long litigation would entail".
A statement from the governing body read: "The FIA has conducted detailed technical analysis on the Scuderia Ferrari Power Unit as it is entitled to do for any competitor in the FIA Formula One World Championship.
"The extensive and thorough investigations undertaken during the 2019 season raised suspicions that the Scuderia Ferrari PU could be considered as not operating within the limits of the FIA regulations at all times.
Ferrari driver Charles Leclerc won two races last season, while Sebastian Vettel took the chequered flag once.
Should the Scuderia have been thrown out, the eight teams finishing behind them would be rewarded with a hefty increase in prize money.
Suspicions were raised Ferrari had exploited a grey area in the rules to increase their fuel flow and boost performance. Ferrari team principal Mattia Binotto has always denied any wrongdoing.
The FIA closed the potential engine loophole ahead of the United States Grand Prix in November, before which Ferrari had recorded six consecutive pole positions and amassed three victories.
Ferrari were subsequently off the pace at the Austin race, and the remaining final two rounds of last year in Brazil and Abu Dhabi. They also appeared to be down on power during pre-season testing.
In response to criticism of the confidential settlement, the FIA said the agreement was a "legal tool recognised as an essential component of any disciplinary system and is used by many public authorities and other sport federations in the handling of disputes."
In conclusion, the governing body added: " The FIA will take all necessary action to protect the sport and its role and reputation as regulator of the FIA Formula One World Championship."
