Thousands of students and striking workers clashed with police Saturday as they marched to demand the reversal of a new law they say would make layoffs easier.
Police fired tear gas to break up the crowd of protesters, estimated to number between 6,000 and 7,000, marching after a rally in central Seoul. Some protesters threw rocks at police, but no injuries were reported.
Police arrested 12 workers for taking part in an illegal march.
Many of the marchers were among 373,000 unionized workers around the nation who have walked off their jobs in the nation's largest organized labor strike ever.
The strike has closed down South Korea's shipbuilding and auto-making industries, key pillars of its export-driven economy.
The unions are demanding that the government retract the labor law, passed in a secretive, predawn parliamentary session Thursday by ruling party legislators, with no opposition members present.
"Down with [President] Kim Young Sam!" the protesters shouted to the incessant beat of gongs and drums. Many in a dense fog of tear gas waved huge banners with the union logo stamped in bright colors.
The new law, the result of nine months of hearings, was designed to bring South Korea's labor conditions up to par with those of other economically advanced nations.
A promise to revise the earlier law was part of South Korea's successful campaign this year for admission to the Organization for Economic Cooperation and Development, the Paris-based think tank of rich countries.
The new law grants more labor freedoms, but those rights have been put on hold for several years, while companies can lay off surplus workers, hire temporary staff and replace strikers.
Workers fear that the new law will be used by businesses to begin huge layoffs, something unheard of in South Korea.
Early today, unionized subway workers in the southern city of Pusan joined colleagues in Seoul who walked off their jobs a day earlier, forcing trains to run late. Nonunion workers were called in to help.