U.S. regulators have informed seven auto makers that the air bag recall from Japanese company Takata is most likely to expand.

The National Highway Traffic Safety Administration (NHTSA) has issued a letter to seven car companies, namely Jaguar-Land Rover, Tesla, Volkswagen, Mercedes-Benz, Spartan Motors, Volvo Trucks, and Suzuki asking for the car models that carry Takata parts, the Associated Press reported.

The letter was distributed last week and the agency said that the air bag recall is likely to expand and will cover other vehicles that are not part of the recent recall.

NHTSA specifically wanted to know which car models use Takata air bags that use ammonium nitrate as its propellant.

According to the letter, the Japanese corporation theorizes that the defects may come from the fact that the chemical degrades in time.

A cause has yet to be identified, but experts believe that the chemical used as propellant becomes unstable with exposure to humidity.

Takata air bags are the only air bags in the industry that use ammonium nitrate as propellant, which cast a doubt on how safe replacement products will be.

The expanded recall could also cover 11 companies including Ford Motor Co., Fiat Chrysler, BMW, NissanMotor Co., and Toyota Motor Corp., among many others, according to reports.

So far, the recall already saw over 23 million Takata air bag inflators from 19.2 million U.S.-registered vehicles distributed by 11 different car companies.

The air bags can explode so hard that it can send out metal shrapnel. Reports stated that eight people all over the world have already died from the airbag and hundreds have already been injured.

The NHTSA will conduct a public meeting on Oct. 22 in Washington to talk about the progress of the Takata investigation and decide if it will step up to handle the matters of the recall to hasten the repair process.