The Korean community in Japan is demanding that money in postal savings accounts held by slave labourers during the second world war be returned to them or their surviving relatives.
Tens of thousands of dormant accounts have been found at a branch of Japan Post Bank in Fukuoka City, southern Japan. Men and women brought to Japan during the years of Tokyo's colonial rule of the Korean peninsula were required to open the postal savings accounts, into which a part of their wages were automatically deposited.
The labourers - who worked in mines, shipyards, steel mills and the agricultural sector - did not receive their full pay as the Japanese authorities feared they might use it to help them escape.
In the chaos of the closing days of the war, the account books were never returned to their owners and they were never notified about their savings.
For nearly 70 years the account books have been gathering dust, including throughout the privatisation of the banking arm of the Japan Post Office in 2007.
"If the holder of the account is still alive, then the money should be returned," said Choi Bong-kyu, a spokesman for Mindan, which represents South Koreans living in Japan.
"In addition, if the holder of the title deed is dead or has disappeared, there is a responsibility to identify his or her relatives and return the money to them. The amounts should be converted to their modern-day value."
That could make the accounts worth millions of yen.
A spokesman for Japan Post said the details in some of the account books were no longer legible and declined to confirm the number of accounts that have been found or the amount of money in them.
"The Japanese government failed to convey information on these accounts to their owners in the confusion after Japan's defeat, but never notified us after the war either," Choi said. "And I believe there are more accounts that have not been located."
A spokesman for the South Korean embassy in Tokyo said it was aware of the reports and was conducting an investigation.
Seoul is expected to call on Tokyo to return the labourers' earnings, but difficult negotiations lie ahead as South Korea and Japan signed a treaty in 1965 that renounced claims against Japan for compensation from individuals.
If Japan does fall back on that argument it is likely to further fan the simmering anger of Koreans towards Japan.
The Japanese government warned this month it was ready to take Seoul to the International Court of Justice unless South Korea's Supreme Court overturned a lower court's verdict that ordered Nippon Steel to compensate Koreans it had used as slave labourers during the war.
The Seoul High Court last month rejected Tokyo's long-held position that it has adequately compensated victims of its colonial rule with a lump sum that was part of the 1965 treaty.
The court ordered Nippon Steel to pay back wages and punitive damages, which the company has appealed. If the appeal is rejected the court could order that Nippon Steel's assets in South Korea - including a 5 per cent stake in Korean steel giant Posco - be seized to provide the compensation.