Button has piloted his Brawn to victory in the first two races of the season
Motorsport's governing body, the FIA, is meeting on Tuesday to decide whether Jenson Button's car is legal.
The Formula 1 championship leader's Brawn Grand Prix team, Toyota and Williams use a split-level diffuser.
The FIA rejected a protest by rival teams, who argue the design does not conform to the new 2009 regulations.
But the International Court of Appeal is expected to announce a final ruling on Wednesday and could deduct points from Brawn, Toyota and Williams.
An independent panel is hearing arguments from both sides at the meeting in Paris, where Ferrari's legal representative, Nigel Tozzi QC, has described Brawn GP team boss Ross Brawn as "a person of supreme arrogance".
WHAT IS A DIFFUSER?
It is the rear part of the floor of the car between the rear wheels and under the rear wing
It is crucial to the aerodynamics, and small changes can have a big impact on downforce - and therefore grip and speed
The row broke out when Ferrari, Renault and Red Bull protested against the legality of the split-level diffusers on the eve of the season-opening Grand Prix in Australia, but race stewards in Melbourne rejected their claims.
BMW Sauber then had a similar protest rejected at the Malaysian Grand Prix while McLaren have recently added their weight to the official protest.
Speaking from outside FIA headquarters in Paris, BBC sports news reporter Joe Wilson said: "Rear diffusers this season were supposed to get smaller, but Brawn and a couple of other teams have ended up with bigger ones, exploiting a little loophole in the laws.
"An independent panel of judges, looking at things with a legal mind, may just uphold this appeal - though there will be widespread surprise, if not shock, if Brawn end up losing their points this season."
The protesting teams say the split-level design contravenes a rule that states the diffuser - an aerodynamic body part which aids performance - must have an upper edge that runs in a horizontal straight line.
They also believe the design is negating the main aim of this season's new rule changes, which is to make overtaking easier.
The split-level diffusers generate more downforce at the rear of the car, resulting in a clear performance advantage of around 0.5 seconds per lap.
If the protestors win their appeal the FIA has two options.
It could allow the results of the first two races to stand, with the three teams concerned being forced to alter their cars from Sunday's Chinese GP onwards, or they could remove any points won by those teams in Australia and Malaysia.
Brawn arrives at Paris hearing
British driver Button - who insists his car is "100% legal" - has won both and his team lead the constructors' championship with 25 points, ahead of Toyota on 16.5 points.
The other eight teams have only 17 points between them and Ferrari, the reigning constructors' champions, are yet to get off the mark.
Prior to the hearing, Brawn said he was optimistic the Court of Appeal would agree with the race stewards and sanction the split-level diffuser design.
"I would just be surprised if the appeal court can make judgements on technicalities - it's quite a complex technical matter," he told BBC Sport.
"You can't be 100% confident but I hope common sense prevails on their side."
If the judges rule the diffusers are legal, then the seven teams who are running without the split-level diffusers are expected to try and incorporate the design into their cars as soon as possible.
Setting about such a radical redesign with the season under way will not be easy.
Many of the teams running with regular diffusers argue the cost of making the changes is too great, especially during a climate of cost-cutting within the sport in the face of the global economic crisis.
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