Over 600,000 salaried workers in South Korea reported an annual additional income surpassing 20 million won ($15,200), aside from their regular salaries, according to data released by the National Health Insurance Service on Monday.

According to NHIS data released by Rep. Choi Hye-young of the main opposition Democratic Party of Korea, the extra income of salaried workers came from bank interest, stock dividends and rental revenue.

The number of salaried workers getting extra income consisted of about 3 percent of the total, which is about 20 million, who are enrolled in the National Health Insurance program and who pay monthly premiums based on their income and assets. Those salaried workers include workers in business, civil servants, and teachers.

The number of those making additional income more than 20 million won annually has been on the rise, marking 194,738 in 2019, 229,731 in 2020, 264,670 in 2021, and 587,592 in 2022.

In the case of salaried workers, monthly premiums for public health insurance services are determined based on their monthly salary. The monthly subscription rate for salaried workers is 7.09 percent. But if their additional income exceeds 20 million won per year, they have to pay additional monthly premiums, about 200,000 won monthly.

By law, all Koreans are required to join the insurance scheme. All foreign nationals residing in Korea for more than six months are also required to enroll in the insurance program.