By Agence France-Presse
The monk in his forties is seeking 8.6 million yen ($78,000) from his temple on Mount Koya, a World Heritage Site also known as Koyasan that regarded as one of the most sacred Buddhist sites in Japan.
The plaintiff began working at a temple there in 2008 and became depressed around December 2015, according to his lawyer Noritake Shirakura.
"If you work as a monk, too often you work without work-hour management," Shirakura told AFP.
"You provide labour, but you are told it's part of religious training. And if it's training, you must endure even it causes you significant hardship."
"Through this case, we will argue that such a notion is outdated," he said.
Shirakura declined to name his client or the temple being sued, saying the man wanted to preserve his anonymity so he could eventually return to his job or find a position elsewhere in the small community of Buddhist monks.
The case argues that the monk was forced to perform paid labour far beyond his spiritual duties, and at times worked for more than two months straight.
In 2015, when the Koyasan area celebrated its 1,200th anniversary, he was forced to work for up to 64 days in a row to handle a surge of tourists to the site, Shirakura said.
Some days, he worked 17 hours straight, performing various temple functions including attending to visitors, the lawyer said.
The monk has already won the backing of a local labour bureau, which acknowledged that the long stretch of work days without holiday met the definition of overwork.
The case is a rare, public labour dispute involving the Japanese spiritual sector.
In 2017, Kyoto's renowned Higashi Honganji temple was forced to publicly apologise for failing to pay overtime compensation and engaging in work-place harassment.
Overwork is a major problem in Japan, and death by overwork is a recognised phenomenon that even has its own word in Japanese -- "karoshi."
A government report released last year found there had been 191 cases of "karoshi" in the 12 months to March 2017, and that more than seven percent of Japanese employees logged over 20 hours of overtime a week.
Prime Minister Shinzo Abe's government has introduced reforms intended to tackle the problem of overwork, but family members who have lost loved ones to the problem argue the measures fall short.