Kobe Steel President Hiroya Kawasaki warned on Thursday there may be more cases of falsified product data, in a sign the unfolding scandal may worsen.
The company has already admitted that products were sold to about 200 firms with false data about their strength and durability.
Toyota, Mazda and General Motors are among the firms affected.
The Japanese government wants the steelmaker to report on the result of its safety checks within two weeks.
Mr Kawasaki told reporters on Thursday that Japan’s trade ministry also wants Kobe Steel to provide reasons for the data fabrication and prevention measures within a month, Reuters said.
Kobe Steel revealed on Sunday that some aluminium and copper products were sent to customers with false quality data. It admitted the falsifications may have started a decade ago.
Since then the embattled firm has seen its shares plunge nearly 40% – wiping more than $1.5bn (£1.1bn) off its market value.
Kobe Steel told the BBC that dozens of employees were involved in the falsification of data on its products.
“There were tens of employees involved. It seems in some cases quality control was undertaken by veteran employees who had lots of experience, highly trusted within the organisation, and somehow these discrepancies slipped by them,” company spokesperson Gary Tsuchida said.