Shares of Japanese car maker Suzuki Motor have tumbled by as much as 15% on reports it may have conducted improper fuel economy testing.

Japanese media reports cited unnamed sources saying that Suzuki had found a problem with its testing method.

Chairman Osamu Suzuki will present a report to Japan’s transport ministry later today, Kyodo news agency said.

It comes after Mitsubishi’s admission last month that it had falsified fuel economy data for its vehicles.

In the wake of the Mitsubishi scandal, Japan’s transport ministry had ordered all of the country’s car makers to present their compliance with government testing methods.

Wednesday is the deadline to present those compliance reports.

Suzuki has declined to comment on the allegations but has announced a news briefing later in the day.

Car makers in the spotlight

Volkswagen has admitted to cheating emissions tests in the US. Authorities found the German car maker was installing a cheating software in its diesel vehicles that could detect when the cars were being tested and would change carbon dioxide emission levels accordingly to improve the results.

Mitsubishi Motors has admitted it had falsified fuel economy data for the past 25 years. Breaking Japanese test rules meant the car maker was able to advertise its vehicles as being more fuel efficient than they actually were.

Nissan has been accused of having some of its UK-built Qashqais fitted with so-called emissions defeat devices. The company has denied the allegations.