Japanese automaker Daihatsu Motor suspended operations at three of its four assembly plants in the country on Monday in the wake of revelations of test data irregularities. The three plants are in Shiga, Kyoto and Oita prefectures.

The firm plans to suspend the remaining plant in Osaka on Tuesday.

The carmaker announced last week that it would suspend domestic shipments of all models following the discovery of 174 additional data irregularities for 64 models. The data was used to obtain government certification.

The four plants produced more than 920,000 vehicles in fiscal 2022. Suspending operations for a month would cause a drop in annual output of about 70,000 units.

It remains unclear when Daihatsu will restart the plants. The data irregularities are likely to affect not only the firm's management but also regional economies across the country, including its business partners and subcontractors.