"Several" Ferrari rivals have asked the FIA to look into the legality of the Italian team's engines.
After the latest Ferrari upgrade, Mercedes team boss Toto Wolff said the power produced by the Maranello-made power unit is "ridiculous".
'Impossible to accomplish legally'
"Several teams have called on the FIA to verify that the power unit is legal," Germany's Auto Bild reported.
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An unnamed Ferrari rival is quoted as saying: "The absurd advantage is impossible to accomplish legally, because the technology is already very well developed.
"Ferrari cheats and the FIA knows it. But it doesn't matter, because it would be a huge scandal."