Formula One's international court of appeal met today to decide the legality of the Brawn GP car that took Jenson Button to victory in the first two races of the season.
Champions Ferrari, Red Bull, Renault and BMW-Sauber have appealed against stewards' decisions in Australia and Malaysia that the rear diffusers used by Brawn, Toyota and Williams were legal.
A verdict is not due until Wednesday afternoon, by which time the teams will already be in Shanghai preparing for Sunday's third round of the season in China.
If the appeal is upheld, the championship could be thrown into turmoil with the court having the power in the most extreme scenario to overturn the results and strip Button of his wins.
If not, the Mercedes-powered Brawns can be expected to keep on winning while other teams race to catch up with radical redesigns of their cars.
McLaren, who also use Mercedes engines, were attending the hearing in Paris as well, but their representatives were not expected to speak despite sharing the view of the protesting four teams.
Ferrari were represented by former title-winning designer Rory Byrne, who was a close colleague of Brawn principal Ross Brawn at the Italian team, and chief designer Nikolas Tombazis.
The controversy centres on the rear diffuser, which channels the air cleanly under and out of the rear of the car to create maximum downforce.
Rivals claim the 'double-decker' or 'split-level' ones used by Brawn, Toyota and Toyota-powered Williams break the spirit of the rules.
Brawn, who have been comfortably quickest in both races since they emerged from the remains of departed Honda last month, and Toyota are first and second in the constructors' standings.
"This decision will have an enormous impact on the championship," Ferrari's 2007 world champion Kimi Raikkonen, whose team have yet to score a point this season, said on his website (http://www.kimiraikkonen.com).
Renault's double world champion Fernando Alonso warned last month that Brawn could run away with the championship.
"If the diffusers are legal, the Brawns are going to be nearly unreachable for any other team," said the Spaniard after the Australian Grand Prix.
Brawn, the former Ferrari technical director before moving to Honda and then taking over the Japanese team in a management buyout, expected the court to uphold the stewards' decisions.
"You can't be 100 per cent confident," he told the BBC before attending the hearing.
"But I hope that common sense prevails on our side and the appeal court judges that there is a mechanism, a procedure, a policy and that it was followed properly and we should be left to get on with it."
While rivals say the diffusers are illegal, they are also working on their own versions in case the appeal is rejected.
"We cannot sit back and wait until the court of appeal is held and we have a decision," BMW-Sauber team boss Mario Theissen said last week. "We have to work on it and we are spending money on it."