It's understood that several teams have written to the FIA seeking clarification about aspects of the design of Ferrari's current power unit.
According to reports from Autosport the teams want to confirm whether the engines are within the rules before deciding on whether to develop similar concepts.
The FIA itselfresponded that it has "received no protest from any competitor regarding any current designs" and that it "continues to monitor all parameters relating to conformity of power units."
Ferrari has made a significant step forward in performance in recent races. After struggling in the first half of the season, the SF90 has been the car to beat ever since introducing aerodynamic upgrades following the summer break.
But rivals believe that this year's Ferrari has always had an "unbelievable" straight line speed advantage amounting to up to eight tenths of a second per lap, ever since pre-season testing.
One high-placed team source is said to have described this level of performance compared to their rivals as "ludicrous". However Ferrari principal Mattia Binotto insisted that the gap was "not as big" as people were saying.
While the improved performance came too late for Ferrari to prevent Mercedes clinching their sixth constructors championship at Suzuka, teams are worried that Ferrari will carry its current speed superiority into 2020, and prove unstoppable.
But engineers are still scratching their heads trying to work out precisely what it is that Ferrari have been able to do with their power units to give them such an edge over those from Mercedes, Renault and Honda.
©Ferrari
One suggestion is that a controlled leak of oil from the intercooler is providing a brief power boost.
While such a leak is permitted, the rules state that it "must not intentionally make use of the latent heat of vaporisation of any fluid with the exception of fuel for the normal purpose of combustion in the engine".
It's not the first time that Ferrari has been challenged over the legality of its designs. Last year protests were lodged against the way it had implemented its ERS and battery storage systems, but the FIA gave Ferrari the all-clear and said that it was "satisfied" the systems were within the regulations.
The FIA is already conducting a review of the legality of Renault's pre-set lap distance-dependent brake bias adjustment system, after a formal protest was lodged by the Racing Point team following the Japanese Grand Prix.
In his post-race debrief, Formula 1 chief Ross Brawn admitted to being puzzled by Racing Point's allegations.
"The Stewards decided not to rule on such a complex matter in Japan, as it needs a careful investigation by the FIA," said Brawn.
"But it’s true that this question hovers over a result that was like finding water in the desert for a team that, compared to last year, have not made the progress they might have expected, and who are currently being beaten by their customer team McLaren."
Furthermore, Ralf Schumacher told Sky Sports Germany that Renault's rumoured system could provide a "big advantage" during a race if it was proved to exist.
"The driver is normally responsible for adjusting the brake balance," he explained. "If it is happening automatically you could brake later and take more speed into each corner.
"An automatic system controlled electronically could do it much better and faster than the driver can manually," he said after news that the FIA had impounded steering wheels and the ECU units from the R.S.19 in Suzuka for detailed analysis.
"The suspicion must be reasonable because it’s an unwritten rule that you don’t accuse another team of something like that unless you’re 100 per cent sure.
"If they’re right, it’s a catastrophe for Renault," he said. "As a works team that would be very questionable. They’d have to rethink everything,"
The protest has been compared to the notorious 'Spygate' incident involving McLaren which saw the team fined and excluded from that year's constructors championship.
However Schumacher said he didn't expect a quick ruling on the matter from the governing body.
"The FIA already seems overwhelmed with the simplest decisions, and this is definitely a mammoth task," he said. "They need to be completely sure, because it would be a huge setback for Renault."
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