SEOUL, South Korea (AP) _ South Korea's largest auto components supplier partially resumed operation at its seven plants Friday, one day after police broke up an 18-day-old strike.

But Mando Machinery Corp. said normal operation was at least three days away as hundreds of workers were in police custody for questioning and many others refused to return to work in protest against the police raids.

Police planned to arrest at least 30 active union members on charges of using violence and organizing illegal strikes.

Mando is a monopoly supplier of air conditioners, heaters, alternators and other key components for Hyundai Motor Co. and other domestic automakers.

Its strike has hampered operation at Hyundai, South Korea's No. 1 automaker, which was recovering from its own 36-day-old strike that ended just last week.

In Thursday's coordinated dawn assaults at Mando's plants around the country, some 8,000 riot police used bulldozers and tear gas to break through barricades and disperse strikers protesting layoffs.

It was the first use of police force to break up a labor protest under the new government of President Kim Dae-jung. Layoffs are legal but new to Korean workers, long accustomed to lifetime employment.

Mando's 4,300 unionized workers went on strike Aug. 17 to protest the company's plan to dismiss 1,090 employees amid a severe slump in the auto industry.

Authorities outlawed the strike because the union did not submit to mandatory government mediation.

Mando sold $1 billion in car components last year, 80 percent of them to Hyundai.