Rivals of the Williams, Toyota and Brawn GP teams told the FIA's International Court of Appeal on Tuesday that there was no doubt the rear diffusers used by trio were illegal.
Ferrari, Renault, BMW Sauber and Red Bull have all appealed against the decision by the Australian and Malaysian Grands Prix stewards to deem the 'diffuser gang's' cars within the scope of the 2009 technical regulations.
Ferrari's legal representative Nigel Tozzi told the court in Paris on Tuesday there was no doubt the teams have exploited a loophole in the regulations to use an illegal device.
"Anyone with a command of English will tell you it is a hole, so do not let someone attempting to be clever with words defeat the express purpose of the rules," Tozzi was quoted as saying by the Press Association.
"The appeal is not because we have not made the most of an opportunity, but because Brawn, Toyota and Williams have not acted within the regulations."
Renault's representative Andrew Ford said the sport's governing body had already concluded the design was illegal, and that was the reason why the French team decided not to use it.
"It is not that Renault missed the boat, as Brawn have pointed out, it is because the FIA said it was illegal. It was at that point the diffuser was abandoned," said Ford.
Brawn GP has won the first two races of the season and the result of today's hearing could completely change the championship situation.
If the ICA decides the diffuser is legal, the British team looks certain to continue at the front until rivals copy the design and catch up.
If it's decided that the "double-diffusers" contravene the rules, Jenson Button could face the prospect of losing his two victories.
Team boss Ross Brawn said he was optimistic the decision would favor his team.
"You can't be 100 percent confident," Brawn told the BBC. "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."
The verdict is not due until Wednesday afternoon.