South Korea said Tuesday it will ban foreigners and overseas Koreans entering the country to seek work from joining its health insurance program immediately upon arrival, in a bid to revise a legal loophole that had allowed some nonpermanent residents to exploit the system.

The current National Health Insurance Act allows foreign nationals and Koreans living in other countries to qualify for the self-backed national health insurance scheme after residing here for at least three months.

Those who the government deems “will clearly stay for three months or more” -- for reasons including studying, marriage and work -- are allowed to sign up on the day of arrival.

But the revised version of the act -- kicking in Oct. 1 -- will exempt those with work visa from the list of people who can get immediate permission to get health insurance, the Health Ministry said. The new measures will not apply to national health insurance provided through employers.

This is to prevent some foreign visitors from taking advantage of the insurance program by pretending to look for jobs while leaving the country once they receive subsidized medical care, according to officials.

Last year, a 55-year-old man reportedly received 170 million won ($142,000) worth of benefits from the insurance program three months after coming to Korea. He and his son left the country less than a year after the surgery.

Unlawful medical fees provided for foreign nationals from 2011 to June 2015 came to 20.8 billion won, according to Rep. Moon Jeong-lim of the ruling Saenuri Party.

Korea’s health insurance program has also seen an increasing deficit from providing care for foreign nationals and overseas Koreans, which went from 62.7 billion won in 2010 to 110.2 billion won in 2014.

As of 2014, 184,800 non-Korean citizens were in the national health insurance program. They received 155.8 billion won in benefits while only paying 45.6 billion won in insurance fees.

Lawmakers have said that while the deficit is partly due to cherry-picking by some foreign nationals, it is also due to questionable government policies, including one to lure more students from other countries. As part of the Park Geun-hye administration’s campaign to host more foreign students, the government has reduced insurance fees for foreign students with D-2 or D-4 visas, while making signing up for the insurance mandatory.

By Yoon Min-sik (minsikyoon@heraldcorp.com)