Business lobby groups on Monday raised concerns over illegal and violent labor protests, calling for stern action against a clash that erupted between protesters and riot police at Hyundai Motor’s Ulsan plant during the weekend.

On Saturday, some 2,500 activists and union members, who were visiting the plant to support irregular workers there, attempted to take over a factory building and clashed violently with police.

Following the clash, which led to dozens of injuries, Hyundai Motor on Monday filed complaints against 13 people for interfering with business and using violence.

“We urge the government to impose heavy punishment on those who led the violent clash. We also ask the labor circle to stop illegal activities and join talks for resolution,” said the Federation of Korean Industries in a statement.

The business lobby also criticized the police for failing to take prompt action before several people were injured during the clash.

The Korea Employers Federation put pressure on Shin Seung-chul, newly-elected president of the Korean Confederation of Trade Unions, the nation’s largest umbrella labor group.

“We had high expectations about the new leader who has emphasized communication. But it was the KCTU that led the extreme activities,” the group said in a separate statement. Shin was elected in a vote last week.

The warnings from the business groups come ahead of the annual “hatu,” massive labor strikes in the summer season. Industry watchers say companies may have wanted to take preemptive action before the strike season.

Hyundai Motor said Monday that it will respond to the violent clash strictly, hinting that it could consider another round of complaints against people who were involved in the violence on Saturday.

The Ulsan plant was forced to suspend operations for about 20 minutes on the day of the clash, the carmaker said.

By Lee Ji-yoon (jylee@heraldcorp.com)