The counterfeit air bags "look nearly identical to certified, original equipment parts," the National Highway Traffic Safety Administration said in a statement.
The counterfeit air bags can even include insignia of major automakers. The problem is, in NHTSA testing, the air bags that were not certified "showed consistent malfunctioning ranging from non-deployment of the air bag to the expulsion of metal shrapnel during deployment," the agency said.
The NHTSA advised consumers who had been in an accident in the past three years and had air bags replaced in independent repair shops, as opposed to dealerships, have their equipment inspected and have non-certified air bags replaced.
Consumers were advised to contact a call center. The NHTSA has posted a list of call centers at www.SaferCar.gov.
"Anytime equipment that is critical to protecting drivers and passengers fails to operate properly, it is a serious safety concern," Transportation Secretary Ray LaHood said in a statement.
"We want consumers to be immediately aware of this problem and to review our safety information to see if their vehicle could be in need of inspection."
The NHTSA said other consumers at risk include those who purchased a used car that may have sustained a prior air bag deployment, owners pf cars designated as salvaged, rebuilt or reconstructed, and people who bought airbags from non-certified sources.
The agency specified eBay as a possible source of counterfeit air bags and said to beware of any airbags with "unusually low prices," especially if they cost under $400.