The latest row engulfing Formula 1 could end up going before another hearing after Red Bull and Ferrari launched official protests against Mercedes, alleging the team breached rules by conducting in-season tyre testing with Pirelli following the Spanish Grand Prix two weeks ago.
The three teams and Pirelli answered questions from stewards following the Monaco GP on Sunday, which was won from pole position by Mercedes driver Nico Rosberg ahead of Red Bull pair Sebastian Vettel and Mark Webber.
Following the hearing, motorsport's governing body said in a statement that "the stewards (present) will write a report to the FIA who may bring the matter before the International Tribunal."
The FIA gave no further details when this might happen. The next race is in two weeks' time in Canada. In a further statement, the FIA warned Mercedes over its conduct and said its tribunal "may decide to inflict penalties that would supersede any penalty the stewards of the meeting may have issued."
Earlier, the team principals of Red Bull and Lotus -- which did not lodge a formal protest -- expressed their annoyance at what they felt was secretive testing by Mercedes.
"We feel it's not in line with the rules," Red Bull's Christian Horner said. "We just want clarity."
Mercedes has been fast in qualifying -- securing a fourth straight pole for Monaco -- but had struggled with durability during races and Rosberg's win was its first of the season.
Rosberg would not be drawn on the issue, saying only "you'll have to ask Pirelli about this issue. I don't want to comment" but Mercedes team principal Ross Brawn spoke up.
"It wasn't a secret test," Brawn said. "It was up to Pirelli to spread the information. It wasn't up to us, it was their test. Pirelli has been asking teams to help them out for 12 months and people haven't been supporting them."
Mercedes' motorsport director Toto Wolff backed that view.
"Everybody speaks about everything these days," Wolff said. "We left everything there, the garage, the buses, the trucks, all the engineering offices. Nothing was secret."
Like Horner, Lotus principal Eric Boullier underlined that the testing fell outside of regulations.
"At the end of the day it's a breach of the sporting code," he said, adding that he found out about the tests on Saturday night. "If they did it, I think it is maybe because they think they could get an advantage."
In agreement with Mercedes, Pirelli conducted those tests after the race in Barcelona.
Although this is not strictly permitted under the sport's rules, there is a grey area because Pirelli insists its contract allows it to conduct private tests with teams under special circumstances.
"It's a situation we need clarification on," Horner said.
Boullier backed him up by saying that, even if there was an agreement in place, it was still unfair on other teams.
"Whatever permission is given, it should be allowed to everybody, or at least to make it aware to everybody and not testing on your own somewhere," Boullier said, adding that Pirelli had not offered Lotus the same opportunity -- although Lotus has been one of the rare teams not to heavily criticize Pirelli's fast-degrading tyres this season.
Pirelli's head of motorsport, Paul Hembery, maintains there has been no wrongdoing.
"We are allowed to do a 1,000-kilometre tyre test with any team," he said prior to the race. "In the World Rally Championship contract it's exactly the same. We can do it with a representative car."
The FIA confirmed that it had been approached by Pirelli earlier this month, but that the agreement for private testing only applies if "every team is offered the opportunity" to do likewise, which is not the case.
"The FIA received no further information about a possible test from Pirelli or from Mercedes," the FIA said. "Furthermore, the FIA received no confirmation that all teams had been given an opportunity to take part in this test."
Hembery said the testing was to look at possibilities to develop next year's tyres -- providing Pirelli is still the official manufacturer -- and in no way gave Mercedes any advantage for Monaco.
"Absolutely not, because it's no relevance to what's happening here," he said. "Mercedes haven't a clue what on earth we were testing in reality."
Pirelli has been under pressure in recent weeks because of its shredding tyres -- with nearly 80 pit stops at the Spanish GP leading to chaotic scenes.
Horner and championship leader Vettel have been the fiercest critics, and the Italian manufacturer still does not have the backing of all teams -- or any word from the FIA -- over a new contract for next season. Pirelli has pledged to make modifications at next month's race in Montreal.
The fact that Mercedes has been struggling for race pace, and that Pirelli has been trying to improve the resistance of its tyres, seemingly gives extra meaning to the private testing.
"They've both cars on the front row of the grid, so it's not hurt," Horner said.
However, Mercedes had been the best in qualifying in the three races before the tests, anyway.