Red Bull's Christian Horner made a surprise appearance in Paris on Thursday as the 'test-gate' hearing began.
But also at the FIA's Place de la Concorde headquarters were representatives of McLaren and Williams, as the governing body's lawyer clearly accused Mercedes of breaking the rules with its highly controversial Barcelona test last month.
"Any running on the track is deemed to be testing," the FIA's lawyer said. "It is difficult to say that Mercedes gained no benefit," he added.
The FIA also alleged that Mercedes and Pirelli were "very odd" in how they went about seeking permission to test, having made "informal" calls and emails to Charlie Whiting and the governing body's legal department, but then going ahead with the test without obtaining clear answers.
Mercedes' lawyer hit back by arguing the Brackley based team did not actually break the rules, because the sporting regulations say only that a team may not 'undertake' a test.
"It is irrefutable it was a test undertaken by Pirelli," he said.
The Mercedes lawyer also accused Ferrari of doing more than 1000 kilometres of testing in the weeks before the Barcelona session, while admitting that having Lewis Hamilton and Nico Rosberg wear all-black helmets was a "regrettable" decision.
"We acknowledge this aspect was bound to raise suspicion," he acknowledged.
A bullish Pirelli, meanwhile, argued that it fully complied with its contract with the FIA, and insisted it cannot be punished because it is not a team or driver.
F1 holds breath for 'test-gate' hearing
The F1 world is holding its collective breath ahead of the 'test-gate' hearing in Paris on Thursday.
Predictably, rumours are swirling.
Germany's Auto Motor und Sport claims Mercedes boss Ross Brawn might be armed not only with an email from Charlie Whiting, but a separate document in which the highly controversial Barcelona test is green-lighted by the FIA's legal department.
But also rumoured is that it will be shown that Mercedes, and possibly also Pirelli, were clearly in the wrong, in which case severe penalties could await, and heads could roll.
"Most people who are talking do not know the facts," Mercedes' Toto Wolff, who will not be in Paris, is quoted by Kleine Zeitung.
Indeed, Wolff has been busy in the last few days, and fellow team shareholder Niki Lauda admitted to Blick newspaper he spent "the whole Montreal weekend trying to prevent the (tribunal) process".
Wolff's efforts of the last days, including meetings with Bernie Ecclestone in London, and Jean Todt in Paris, were also in vain, according to Sport Bild.
So, also to appear before the 12-judge panel on Thursday morning will be Pirelli's Paul Hembery.
With Brawn representing Mercedes alone, Wolff denied the team's British boss - whose future successor Paddy Lowe is already working at Brackley - is the scapegoat.
"Ross Brawn is not being sacrificed in Paris. That's not in my nature," Wolff told Bild.
"Ross doesn't need someone like me there, holding his hand."
However, there is speculation that in the event of a high penalty - like hefty points deductions and a two-digit million fine - Brawn might voluntarily step down.
McLaren team boss Martin Whitmarsh is quoted by motorline.cc as suggesting that a penalty, if any, "should be decided by the FIA".
"But usually a sporting penalty should be imposed for a sporting offence," he added, suggesting a mere fine will not be enough.
Former driver Marc Surer agrees: "Only a fine would mean that a team like Red Bull could also test for 1000 kilometres -- it would be relatively expensive, but doable.
"So there must be a sporting penalty," he insisted.
Pirelli-factor hurting F1 ticket sales - Button
Jenson Button thinks the economy and an 'after you' style of racing in 2013 has hurt ticket sales ahead of the British grand prix.
Writing in the Independent this week, F1 business journalist Christian Sylt said lower than usual ticket sales for the weekend's Silverstone race is because fans have rebelled against price increases.
A circuit spokesman admitted sales "aren't that strong".
Some of the other reasons for the slump could be because Button and Lewis Hamilton are unlikely to win, and also because ticket holders were actually turned away from qualifying last year amid the weather chaos.
Button thinks the economy is one definite factor.
"To sell out here would be very impressive but are there that many people who can afford to come?" he is quoted by the Guardian newspaper.
"I don't think people are walking away from the sport. If you look at every sporting event, it is not as strong as maybe it was last year. That is just the way the world is at the moment."
A factor specific to F1, however, could be the questionable spectacle of the 2013 formula, caused mainly by drivers having to race off the pace to look after Pirelli's fragile tyres.
"I agree that some of the racing hasn't been action-packed," Button said.
"It has been a lot more 'After you, sir, because I am looking after my tyres'. But there have been good races," he insisted.
Le Mans would welcome Mark Webber - McNish
Former F1 driver Allan McNish thinks the world of Le Mans would welcome Mark Webber with open arms in 2014.
With his Red Bull deal expiring, and the world champions weighing up the candidates to replace him, 37-year-old Australian Webber has been linked with Porsche's return to prototype sports car racing.
"If Mark did decide to come we would all embrace him with open arms -– until the first corner," Scot McNish, who raced in F1 with Toyota in 2002, joked to the Huffington Post.
"He wouldn't want it any other way," smiled McNish, now a top Le Mans driver for Audi.
"He's a hard charger, he's intelligent, he's a thinker, he's a nice person, he'd be good in the paddock," McNish said of Webber, who raced at Le Mans late last century with Mercedes.
The fabled 24 hour Le Mans race takes place this weekend, and McNish thinks the event can compete head-to-head with formula one.
"I think sports cars has offered manufacturers a place where they can develop a technology at a good, sensible cost," he said.
"They can race in a high profile race, Le Mans, which matches any F1 race without question and it's got a world championship.
"Look at Renault -- they've won the F1 world championship for quite a few years but no one knows. They all think it's a Red Bull."
McNish also said Le Mans has become a "viable" option for drivers of F1 pedigree like Kamui Kobayashi and Bruno Senna, and questioned whether formula one has taken the right direction with its tyre-dominated racing.
"It's very odd the way it is in formula one now," he said.
"I was looking at the laptimes from the Bahrain GP and noticed that they were basically the same as our race laptimes there -- for a car that is 300kg lighter.
"I think F1 has tried quite hard over the past few years to become a spectacle, to get the fans to enjoy wheel to wheel racing.
"I think it's positive to do that but they might have gone a little bit too far," added McNish.
Hulkenberg hints Force India exit not 'right decision'
Nico Hulkenberg has admitted for the first time that moving from Force India to Sauber over the winter may not have been the "right decision".
Until now, the 25-year-old German has defended his move on the basis that Swiss team Sauber, currently in a performance slump, has the potential to revive its podium-winning form of 2012.
But, now with more of a third of the 2013 season in the past, Hulkenberg has acknowledged Sauber is in "a difficult situation" with its C32 car, while Force India is in the top-five of the championship, ahead even of McLaren.
"Of course this is not what I had imagined, and not what the team imagined," Hulkenberg told Speed Week.
"Clearly we are not where we want to be and where we should be.
"But unfortunately that's formula one -- when you make decisions, there is never a guarantee that it's going to be the right one.
"What we have to do now is to keep looking ahead and get the best out of the season."
Hulkenberg admitted that being passed or beaten by a Force India in 2013 hurts.
"To be honest it hasn't happened on the track, but due to strategy or in the pits, of course it does (hurt). I would like to have a faster car."
Meanwhile, Jenson Button has said that, amid McLaren's slump, it is no surprise Force India has raced past the British grandee.
"Part of their car is from us, part is from Mercedes, so they are going to do well," he told British newspapers.
Maldonado not threatened by rising rookie Bottas
Pastor Maldonado insists he does not feel threatened by the rising form of his rookie teammate Valtteri Bottas.
Young Finn Bottas grabbed the headlines in Montreal recently when he qualified third, amid a profile already on the rise due to his form alongside Venezuelan Maldonado, the more experienced driver and 2012 Barcelona winner.
But Maldonado said on Wednesday: "The conditions benefitted Valtteri in Canada.
"It doesn't mean he's faster and I'm slower. Our car is quite difficult, but I don't need to prove anything to anybody," the 28-year-old, who like Bottas is yet to score a single point in 2013, is quoted by Brazil's Globo Esporte.
Indeed, Maldonado argues that Williams is leaning on him too hard, due to Bottas' inexperience.
"They rely too much on me," he said.
"In fact, I am responsible for all the technical testing of the car because I have more knowledge and experience with the team," added Maldonado.
His comments coincide with rumours Maldonado, backed by millions in sponsorship from PDVSA, has been earmarked by Lotus as a potential successor to the possibly Red Bull-bound Kimi Raikkonen.
Maldonado insisted: "It's not the time to plan where I will be in 2014.
"I sincerely hope to continue for a few more years at Williams. It is the team that gave me the opportunity to be in formula one, and I got my first and so far only victory with them.
"I believe we have the potential to win more with this team," he added.