TOKYO - Japanese advertising giant Dentsu, under fire for gross workplace malpractice leading to the suicide of an overworked rookie on Christmas Day 2015, will pay 2.4 billion yen (S$29 million) in overtime wages to its workers next month.

The sum is for the two-year period ending March, 2017, the firm said on Tuesday (Nov 28), as it acknowledged that its workers have long hewed to the unspoken norm of covering up their overtime hours in the name of "self-improvement" to help the company dodge suspicions of labour inspectors.

Dentsu was last month slapped with a token fine of 500,000 yen for flouting labour laws leading to the death of Ms Matsuri Takahashi, 24.

It has since urged workers to retrospectively report their unpaid overtime hours, and taken measures such as switching off lights at its headquarters at 10pm and removing from its employee handbook the mantra "Once you start, don't quit - even if it kills you".

Ms Takahashi's death has become a cause celebre against gruelling overtime, and sparked a deep rethink in Tokyo of how to curb the deep-rooted problem that has time and again led to karoshi, or death by overwork.

Japan is considering new laws to cap overtime work at 100 hours a month and 720 hours a year. But to work overtime for 100 hours in a standard month of 20 work days - assuming employees do not clock in on weekends - will mean working an extra five hours a day, on top of the standard eight-hour workday.

This has been criticised as a dangerously high, not to mention arbitrary, standard before a worker's health is threatened.

Ms Takahashi killed herself after being made to work over 100 hours of overtime each month since she joined the company in April 2015, until her death eight months later.

Dentsu was last year named "Most Evil Corporation" in a dubious annual honour given by a Japanese non-profit group to highlight abusive workplace practices among so-called burakku kigyo, or black companies.

This is much like Hollywood has its annual Razzies to recognise the worst of the film industry, and Japan's "award" - a copy of the labour law dictionary - usually goes unclaimed.

This year's list of nominees, announced on Monday (Nov 27), includes public broadcaster NHK. The company confessed last month that it worked 31-year-old political reporter Miwa Sado to death in 2013. She died of heart failure in her sleep, with her phone still in hand as if she was awaiting her next assignment.

The other nominees include Taisei Corp - the main contractor for Tokyo's new Olympic stadium that is now racing against time after a design and budget debacle - and its subcontractor Sanshin Corp. An unnamed 23-year-old male site supervisor, fresh out of university, commited suicide this year after 211 hours of overtime in a month.

"My physical and mental state have been stretched to their limits, and there is no other way out," he wrote in a suicide note.

Other companies such as tech giant Panasonic and the Niigata City General Hospital, which have had karoshi incidents reported this year, also made the list.

Courier delivery firm Yamato Transport was also nominated after it admitted in April to withholding two years' worth of overtime wages to its 47,000 employees, and attributed overworking its employees to meeting a surge in online shopping orders. It coughed out 19 billion yen in retrospect earlier this year.