MADRID — The Formula One championship could be thrown into disarray Tuesday when motor racing's governing body rules on the legality of a car part that has helped Brawn GP's Jenson Button win the opening two races.

Ferrari, BMW Sauber, Renault and Red Bull have all lodged appeals to FIA against the stewards' decision in Australia and Malaysia to allow Brawn GP, Toyota and Williams to race with rear diffusers that allegedly breach new aerodynamic regulations.

The three teams have dominated the opening two races because the diffusers — an under-car device that channels the flow of air from the front to rear — help create greater downforce through corners.

Button leads the championship with 15 points, five more than teammate Rubens Barrichello. Toyota pair Jarno Trulli and Timo Glock are next.

The FIA's International Court of Appeal could annul the start by Brawn GP, the former Honda team which was saved by a last-minute buyout by Ross Brawn and is the first new outfit to win its opening two races since Alfa Romeo in the inaugural F1 season in 1950.

The FIA knew of the three teams' design plans for the diffuser and raised no objection, president Max Mosley even backing the alternative idea.

With F1 welcoming its greatest modification to aerodynamics in more than 25 years, the field has been turned upside down with regular title challengers McLaren and Ferrari at the bottom of the standings.

Ferrari designer Rory Byrne, who has helped Ferrari to six world titles since joining the team in 1997, said the fact that the car's equipment underneath is visible through the rear hole is in breach of regulations that have stood for nearly 15 years.

"If you look at the Brawn car from underneath, you can see the suspension," Byrne told Gazetta dello Sport. "Fully enclosed holes are permitted in the surfaces lying on the reference and step planes, provided no part of the car is visible through them when viewed from directly below."

Brawn says his "conscience is clear" after offering the other nine teams a chance to define this vague area.

"I did explain that I felt we should have a different set of rules to simplify what needed to be done. I offered them, and they were rejected," Brawn said. "We needed to clean the rules up, but nobody was interested. They're interested now."

Ferrari and McLaren said their battle last season for the championship took its toll with their 2009 cars poorly developed, and that to modify the diffuser now would take months.

Whether FIA will overturn a design it initially cleared is uncertain, especially since motor racing's premier sport has been blighted by one controversy after another this season.

McLaren could be banned or suspended after bringing the sport into disrepute for twice lying about a driving incident involving defending champion Lewis Hamilton and Trulli at Melbourne.

The FIA attempted to change the points scoring system before this season only for the teams to rebel and force an embarrassing U-turn.

The Malaysian Grand Prix was also stopped just after the halfway point due to torrential rains after F1 boss Bernie Ecclestone scheduled a twilight start despite the probability of late showers.