Shares in Japanese homebuilder Tama Home Co. plunged in Tokyo on Wednesday after reports the firm's president told employees they'd be punished if they got coronavirus vaccines.

Weekly magazine Shukan Bunshun, citing several unidentified workers, reported that President Shinya Tamaki told managers that he opposed coronavirus vaccines. The report said Tamaki warned that people who received the vaccine would die in five years, while internal e-mails told employees of the reported dangers of 5G phones.

Workers who got the vaccine would be told to stay out of the workplace indefinitely, a punishment that would mean they wouldn't receive pay, the report said.

Shares in Tama Home, one of the country's largest builders of homes, closed down 10%, the biggest decline in more than three years. Trading volume was over 13 times the average, and company was the biggest decliner on the Topix index, which rose 0.8%.

Shares in Tama Home, one of Japan's largest builders of homes, closed down 10%.

In a statement, the company flatly denied it put pressure on workers not to get vaccines, or threatened to punish staff if they did get inoculated, saying posts online and on Twitter that said otherwise were "completely untrue."

"The decision to get vaccinated is up to each individual," the statement said.

Tamaki, 42, became president of the firm in 2018, taking over from his father, founder Yasuhiro Tamaki, now 71. Shares have more than doubled since it was first announced the younger Tamaki would take over.

Vaccinations carried out at workplaces have become a core component of Japan's Covid-19 response, with more than 4.6 million doses administered through a program to enlist corporations to roll out vaccines. After a delayed start, the country is now operating at one of the fastest paces among Group of Seven nations, although only 22% of the country is fully vaccinated.