National Highway Traffic Safety Administration investigators estimate 250,000 cars on the road are affected, and those most at risk are motorists who have had their air bags replaced over the past three years by a repair shop.
NHTSA investigators said dealership repairs are likely safe.
NHTSA Administrator David Strickland called counterfeit air bags "an extreme safety risk."
In 2009, 10News found a Southern California auto repairman filling air bag chambers with newspaper. One of the cars he repaired killed a San Diego teen.
In 2011, California lawmakers made it a felony to fail to properly repair an air bag.
The NHTSA is asking car owners to check the government website safercar.gov for information on how to contact auto manufacturer call centers to learn if their vehicle model is among those for which counterfeit airbags are known to have been made.