Mitsubishi Motors Corp. is likely to be fined about ¥480 million ($4.2 million) for making false claims in sales literature about the fuel efficiency of its cars, a government source has said.

The Consumer Affairs Agency plans to announce, possibly Friday, the fine — the first of its kind under a law revision that came into force last April concerning mislabeled products.

The automaker admitted in April that it manipulated data to make four of its minicar models, including two supplied to Nissan Motor Co., look more efficient than they actually were. The number of models involved later expanded beyond minicars.

Mitsubishi Motors showed better-than-actual fuel economy data in sales catalogs and advertising for those models.

After investigating, the agency apparently decided that Mitsubishi Motors contravened the law by portraying the quality of its products as much better than the reality, the source said on Thursday.

The fine will likely apply to the sale of the affected models from April 1 last year, when the law came into effect, to later that month when Mitsubishi Motors revealed the data manipulation of minicars.

The fine will also likely apply to sales of other models through late August when the company announced data irregularities for other vehicles, the source said.

The agency also plans to order Mitsubishi Motors and Nissan to take measures to prevent a repeat of the manipulation, the source said.