Unionised workers at Hyundai Motor Co and other South Korean car makers said on Sunday they would stop work for two hours this week after more anti-government protests at the weekend injured 100 riot police.
A beef import deal struck between the United States and Seoul has sparked mass street rallies, piling pressure on new President Lee Myung-bak and delaying his plans for business-friendly reforms.
The Korean Metal Workers' Union, representing 230 companies, said that 76 percent of its voting members had agreed to the stoppage on Wednesday to demand a reworking of the beef deal and better working conditions, according to a statement posted on its website.
The metal industry union is under the militant Korean Confederation of Trade Unions (KCTU) which has more than 600,000 members, including Kia Motors Corp and Ssangyong Motor Co. At the weekend, protesters tried to overturn buses blocking the road to the presidential Blue House as they fought with riot police who used water cannon.
Justice Minister Kim Kyung-han said around 100 riot police were hurt in the protests which started on Saturday and carried on through until early on Sunday.
Fifty-five protesters were detained, Yonhap news said. The rallies started in early May over concerns about possible mad cow disease in US beef, and later turned into protests against Lee's policies.
The rallies have turned more violent in recent weeks as militant activist groups have come to the forefront. "Beyond the beef issue, they are now opposed to the implementation of reasonable government policies and denying the identity of the government," Kim, flanked by other ministers, said in a TV broadcast.
But the number of people participating in rallies against the beef deal first reached in April has dropped in recent weeks and surveys said most South Koreans wanted them to end. South Korea allowed US beef back into its market for the first time in nine months last Thursday.
Last weekend, South Korea and the United States said they reached a private-sector deal to restrict trade in US beef to cattle under 30 months old and to forbid exports of parts that are thought to pose a higher risk of mad cow disease.
The protests have led to a nosedive in the popularity for Lee, causing a crisis for his four-month-old government and delaying his plans for business-friendly reforms such as easing restrictions on investment and cutting corporates taxes. Labour groups have been angered by his plans to privatise state-run firms and reform pension systems.