Toyota says it will drop Takata as an air bag supplier.

TOKYO — Customers are quickly rethinking their relationship with Takata, leaving the fate of its big air bag business in doubt.

After months of frustration, carmakers in Japan, Takata’s home market, rushed this week to distance themselves from the company, whose products are at the center of the largest automotive safety recall in history.

On Friday, Toyota and Nissan dropped Takata as an air bag supplier after a similar move by Honda on Tuesday. Other Japanese automakers, including Mazda, Mitsubishi Motors and Fuji Heavy Industries, the maker of Subaru vehicles, said this week that they were considering phasing out Takata’s main air bag technology.

For Takata, those relationships are critical. Air bags are a major part of Takata’s business, generating about 40 percent of its sales. And Toyota, Honda and Nissan are the three largest car manufacturers in Japan.

Akio Toyoda, Toyota’s president, said that the company was “placing top priority on ensuring the safety and confidence of our customers.”

The trouble centers on the ammonium nitrate propellant in Takata’s airbag inflaters. The ammonium nitrate can destabilize, in extreme cases causing the device to explode and send metal fragments into the vehicle. Eight deaths and more than 100 injuries have been linked to the defective inflaters.

U.S. safety regulators this week effectively barred Takata from continuing to use ammonium nitrate, its main propellant. A consent order accompanying a $70 million fine imposed by the National Highway Traffic Safety Administration requires that the company phase out inflaters containing the compound unless it can prove they are safe.

The company reported a net loss of $240 million last fiscal year.