Japan's transport ministry says it will issue a business improvement order to one of the country's leading rail freight carriers for falsifying data related to its car maintenance work.

Japan Freight Railway Company disclosed in September that data had been fabricated in the process of fitting wheels on car axles.

JR Freight said the irregularities included falsifying data on the pressure of the fittings to make sure they met required standards. Similar fabrications subsequently came to light regarding cars at other railway operators.

The transport ministry investigated safety management and other practices at eight railway operators where irregularities were found, in line with the Railway Business Act.

The ministry found that JR Freight did not have any in-house rules on wheel-to-axle fittings, and that the handover of duties among workers, including instructions to rewrite logs, had been conducted verbally.

It says the firm must review its safety management.

Ministry officials say they will hear the company's opinion before formally issuing a business improvement order to JR Freight in line with the Railway Business Act.

The ministry has also issued administrative guidance to seven other companies it investigated, including Tokyo Metro, Keio Corporation, Tokyu Railways and East Japan Railway Company.