The transport ministry launched a special audit of Japan Post on Friday over improperly conducted mandatory alcohol and health checks on delivery drivers.

The audit, based on the motor truck transportation business law, started after it was learned that 75% of post offices offering collection and delivery services across the country had improperly conducted checks. The ministry will consider administrative punishments after carrying out probes.

Investigators conducted an on-site investigation Friday at the Takanawa post office in Tokyo's Minato Ward, with six officials from the Kanto District Transport Bureau entering the office's main entrance at around 10 a.m.

The special audit covers legal compliance in general, so authorities will also search for possible violations other than on the checks.

Japan Post said Wednesday that improper checks had taken place at 2,391 offices across all 13 of its regional branches, out of the 3,188 offices handling collection and delivery services nationwide.

The irregularities included fabricating records without conducting the checks.

Under the motor truck transportation business law, business operators are obligated to confirm whether drivers are under the influence of alcohol before and after work. Violations can result in suspensions of vehicle use at each office.

Transport minister Hiromasa Nakano told a news conference Friday that the ministry will "take strict measures after carefully assessing the facts."

Internal affairs minister Seiichiro Murakami expressed regret over the scandal, saying, "We will take necessary measures after reports on the matter."