The government plans to toughen penalties on automakers who falsify fuel efficiency data in light of the scandals involving Mitsubishi Motors Corp. and Suzuki Motor Corp., a government source said.

As one measure, the Land, Infrastructure, Transport and Tourism Ministry plans to hike fines as high as ¥200 million per case from the paltry ¥300,000 at present, the source said.

It is also considering legislation to imprison corporate managers involved in data manipulation, the source added.

In September, the ministry rolled out new penalties for automakers that manipulate fuel efficiency figures, including production suspensions and fines, but calls are growing to make them tougher.

The government is expected to submit revisions to the Road Transport Vehicle Act when the Diet convenes next month.

The revisions will include a stipulation that allows the government to withdraw approval for vehicles made by automaker who intentionally manipulate data to them look more efficient.

Withdrawal would require the automaker to retest the vehicle in question, which adversely affect its business plans.

Mitsubishi Motors recently admitted that all its models sold over the past 10 years were tainted by fuel efficiency manipulation. It also used improper data when re-testing.

MMC turned to Nissan Motor Co. for help. Nissan became its biggest shareholder in October, taking a 34 percent stake as part of an alliance aimed at helping it recover from the scandal.

At Nissan's extraordinary shareholders' meeting this month, Nissan boss Carlos Ghosn pledged to rebuild trust in MMC and return the loss-making carmaker to profitability. He then became chairman.

Suzuki's testing methods were found to be out of compliance since around 2010. Its leader Osamu Suzuki resigned as CEO after the scandal broke.