The new rules stipulate that car mirrors will have to reflect a one-meter wide strip of the road behind a car.
The regulations, to be implemented from the beginning of 2006, mean that mirrors could grow by up to 20-30mm.
Car designers fear bigger mirrors will spoil the lines of their carefully crafted designs.
"It will become more difficult to find a harmonic way of fitting the exterior mirrors into the design," says Audi designer Garry Telaak.
Increasing the size of car mirrors will have an effect on both the cross-sectional area of a vehicle and drag coefficient.
This could increase a car's fuel consumption at a time when automakers are seeking to improve fuel efficiency to meet their obligations to reduce CO2 emissions.