Japanese officials have raided a Mitsubishi Motors Corporation (MMC) office following the automaker’s admission that it had manipulated fuel consumption test data on four mini-car models to present better fuel economy figures than that achieved.

According to news reports, officials from the country’s transport ministry raided the automaker’s plant in Okazaki yesterday, and proceedings are expected to continue today. Saying Mitsubishi had broken the trust of consumers, the Japanese government stated it was treating the issue as an extremely serious case, and has set an April 27 deadline for the automaker to submit a full report on the matter.

On Wednesday, the company announced that fuel consumption tests had been improperly conducted on the Mitsubishi eK Wagon and eK Space as well as the Nissan Dayz and Dayz Roox, which it has been manufacturing and supplying to Nissan since June 2013.

More than half a million cars are involved in the fiasco – MMC said that up until March this year, it has sold 157,000 units of the eK Wagon and eK Space and supplied 468,000 units of the Dayz and Dayz Roox to Nissan. Mitsubishi said that since it developed the applicable cars and was responsible for obtaining the relevant certification for them, it was the party that conducted the testing.

It’s not the first time MMC has been involved in a scandal, but it’s the first time a Japanese automaker has admitted to misconduct involving fuel economy tests. About a decade ago, the automaker almost came to the brink of collapse following a defects scandal, in which it emerged it had been systematically covering up problems and issues over decades.