Critics contend the Volt is not a true EV (electric vehicle) because the gasoline engine kicks in during a hard acceleration. The Volt features a 4-cylinder gasoline engine which acts as a generator to charge the batteries as the car is driving.

General Motors is in a dispute with critics of its upcoming Chevy Volt, which the automaker touts as an all-electric car but critics say is just a plug-in hybrid.

Critics from publications such as, Popular Mechanics, and Motor Trend magazine contend that the on-board gasoline engine kicks in on the Volt during a hard acceleration - and that makes it a hybrid.

GM calls the Volt an "extended range electric vehicle." The Volt features a gasoline engine which acts as a generator for the batteries that power the electric motor. It is the electric motor that drives the wheels - not the gasoline engine which is there to charge the batteries as the car is driving and extend its range. But the engine can also drive a secondary generator which provides power directly to the motor.

The set-up is similar to the Toyota Prius, which is labeled a hybrid. Its gasoline engine fuels a direct-drive generator that powers the electric motor which drives the wheels.

The Detroit automaker had previously gotten in trouble with critics when it rated the Volt's mileage at 230 miles per gallon (about 1 liter/100 km). The Environment Protection Agency, the arm of the United States federal government which rates vehicle mileage, refused to go along with that rating. Mileage figures on electric cars vary wildly because they depend so much on driving habits. Driven aggressively, the batteries on an electric car can be run down very quickly.

The criticism has been particularly harsh and beyond the usual skepticism of automaker hype. accused GM of lying, titling one of its stories: "GM Lied: Chevy Volt is not a true EV."

The Chevrolet Volt goes on sale in the United States next month. Prices will start at $41,000, not including federal tax credits.

Gallery: GM fights off criticism of Volt