All South Koreans should report their earnings from investments in overseas companies or real estate by June 1, with violators facing fines, the tax office said Monday.

The new rule, which is part of the revised 2013 tax code, marks the first time the government has taken steps to get private citizens to report their overseas investments, the National Tax Service said.

The move is expected to discourage tax evasion and expand the country tax base that can generate new revenue for the state, it added.

From 2011 onwards, companies that made foreign investments or bought property were required to file reports but not individuals.

"Because reporting by individuals was voluntary, only about 20 percent took such steps in 2014, and there was nothing tax authorities could do about the remaining 80 percent," an NTS official said.

For this year, however, the NTS expects some 30,000 people to file earnings reports. Those on the list are people that own at least 10 percent of stocks in a foreign company or have total investments that exceed 100 million won ($92,000).

People who have rented out property or bought real estate last year are also subject to the filing obligations.

The tax office said those who fail to do so or intentionally try to hide earnings can face fines of up to 3 million won and may be subject to a tax audit down the line.

South Korea has set up various arrangements with foreign countries that allow it to get tax- and earnings-related information that can help in a probe. (Yonhap)