YOKOHAMA--The labor ministry sent papers on Mitsubishi Electric Corp. and a supervisor to prosecutors here on Jan. 11 on suspicions that they had an employee work illegally long overtime hours, leading to his mental distress and firing.

The action follows a government crackdown on the practice of illegal overtime, which led a young employee at advertising giant Dentsu Inc. to commit suicide in December 2015.

The Fujisawa Labor Standard Inspection Office, which belongs to the ministry's Kanagawa Labor Bureau, suspects that Mitsubishi and the supervisor, who is in charge of labor management affairs, violated the Labor Standards Law.

“We are taking it seriously," the major electric appliance maker, based in Tokyo, said in a statement. "We will thoroughly implement proper management of working hours again.”

According to the bureau, it is suspected that Mitsubishi Electric had one of its male employees at its Information Technology R&D Center in Kamakura, Kanagawa Prefecture, work about 78 hours of overtime in a one-month period from Jan. 16 to Feb. 15, 2014.

That exceeded the 60 hours agreed upon by company management and the labor union as the monthly upper limit of overtime.

According to statements submitted by the man, the employee, now 31, took a leave of absence from his job from June 2014 due to a mental illness. He was subsequently fired in June 2016.

In November 2016, the Fujisawa Labor Standard Inspection Office recognized that his distress was caused by illegally long overtime hours, which sometimes exceeded 100 a month.

The recognition made it possible for the former employee to be eligible for the government-sponsored workers’ accident compensation insurance program.

The man, who joined Mitsubishi Electric in April 2013, was in charge of research and development of lasers used in household electric appliances. In his workplace, employees were responsible for reporting their work hours.

He said that he was instructed by his superior to make a false declaration of his overtime hours, which fell within the monthly upper limit of 60 hours that was reported to the inspection office by the company.