Automaker shares extended losses as U.S regulators overseeing the replacement of Takata Corp. airbags considered expanding recalls to include Tesla Motors Inc., Suzuki Motor Corp. and five others.

Takata fell 1.2 percent and Suzuki dropped 3.8 percent at the close of Tokyo trading, while the Topix Index slid 4.4 percent. Tesla dropped 3.3 percent in U.S. trading on Monday, Volkswagen AG slumped 7.5 percent and Daimler AG fell 3.2 percent in Germany.

Takata shares have lost almost half their value in the past year as the auto industry has scrambled to replace more than 23 million of the company’s air bag inflators, which can deploy with too much force and spray plastic and metal at car passengers. Chemical propellant used in the inflators appears to be one of many factors contributing to the air bag ruptures linked to at least eight deaths and 130 injuries, Takata has said.

In July, Takata told NHTSA that it continued to supply air bags with ammonium nitrate propellant to Volkswagen and Tesla. The agency sent letters last week to those manufacturers, as well as Mercedes-Benz, Jaguar Land Rover, Suzuki Motor Corp., Volvo Trucks and Spartan Motors Inc., because Takata had identified them as companies it supplied with ammonium nitrate inflators.

NHTSA asked the manufacturers whether they’re contemplating service actions and what challenges they’d face if the agency ordered a wider scope for the recalls. The regulator gave the companies 21 days to respond.

Takata spokesman Hideyuki Matsumoto declined to comment, saying the issues are between NHTSA and the carmakers. Suzuki spokesman Ei Mochizuki said he cannot immediately comment.

NHTSA has so far confirmed Takata’s main findings related to the root cause behind the air-bag failures — that the defect may be related to age, prolonged exposure to high humidity and moisture altering the chemical makeup of the ammonium nitrate inflator propellant, according to an agency official who requested anonymity to brief reporters on a conference call this month.

NHTSA plans to hold a public hearing this fall to present its findings on the cause of the failures and how it plans to proceed, the official had said.