Photo/IllutrationTokyo Labor Bureau employees enter the Dentsu Inc. headquarters in Tokyo at around 9:30 a.m. on Nov. 7. (Reina Kitamura)

Labor ministry investigators raided the offices of Dentsu Inc. on Nov. 7 in search of evidence that could be used in filing criminal charges against the advertising giant after one of its employees died from overwork.

Thirty-two Tokyo Labor Bureau inspectors entered Dentsu's head office in the capital at around 9:30 a.m.

The entire operation involved 88 investigators, with three Dentsu branches in Osaka, Nagoya and Kyoto being simultaneously raided.

The ministry suspects that Dentsu employees regularly worked illegal amounts of overtime, including the young woman who was ruled to have died from "karoshi," or death from overwork.

Dentsu could be prosecuted depending on what evidence is found of it having violated the Labor Standards Law.

The labor bureau and other government bodies first searched Dentsu’s headquarters and several offices with an inspection force of about 30 investigators in October. Investigators asked the company to submit evidence on a voluntary basis.

In the latest search, investigators are authorized under the law to seize detailed data on employees' working hours and labor management records.

“It is true that we are undergoing an investigation. We will be fully cooperating with the investigators,” a Dentsu public relations official told The Asahi Shimbun.

The company has also come under fire for neglecting to take the necessary measures to improve working practices despite having received warnings from labor standard inspection offices in Osaka and Tokyo in 2014 and 2015, respectively.

Matsuri Takahashi, 24, killed herself in a company dormitory in December 2015 after working a huge amount of overtime hours.

The ad agency has had its back to the wall since a Tokyo labor standard inspection office ruled in September that her death was due to overwork.

“Her workload increased sharply, and her overtime hours shot up dramatically,” the ruling stated.