The move came amid worries that the increasing number of illegal residents may hamper the implementation of the foreign work-permit system scheduled to begin Aug. 17.

"Illegal migrant workers who leave Korea voluntarily will be offered a chance to re-enter the nation, whereas those who refuse to do so will be banned from entering the country and their employment opportunities here will be limited," said the statement.

The Justice Ministry officials said the government was considering stronger penalties for companies employing illegal foreigners. Currently, offending employers may be fined a maximum of 20 million won, with the same fine given to workers relative to their period of employment.

Just about a month from the launch of the new foreign-worker system, the number of foreigners overstaying their visas increased from 131,000 in January to 166,000 last month. The government forcast the number to top 200,000 by the end of this year, during the months they are calling a "transitional period."

Some political analysts say the April general elections softened the government crackdown during the first half of the year as the administration was mindful of economically sensitive voters. Seoul officials denied the allegation.

The owners of small and midsize companies have worried about a possible labor shortage as their worksites are typically shunned by Korean jobseekers who refuse to do the so-called 3D jobs-dirty, dangerous and difficult.

Under the foreign work-permit system, Korea is scheduled to accept 25,000 foreigners this year from six countries-the Philippines, Mongolia, Sri Lanka, Vietnam, Thailand and Indonesia.

The system is designed to provide foreign workers with better job protection compared to the current industrial trainee program. The trainee system does not recognize labor rights for foreign trainees, which human rights groups have criticized for leading to abuse.