About 33,000 workers at Kia Motors Corp. stopped work for two hours, and some 45,000 workers at South Korea's largest carmaker, Hyundai Motor Co., planned to do the same later in the day, union officials said.

The partial walkout at the two affiliated carmakers were the centerpiece of a one-day strike by the Korean Confederation of Trade Unions to protest U.S. beef imports and the pro-business policies of President Lee Myung-bak.

The 600,000-member KCTU said about 130,000 people across the nation were expected to join the strike, including workers at textile and chemical factories. It urged members to participate in candlelight rallies against beef imports later Wednesday.

The government has billed the work stoppage as an "illegal and political" strike unrelated to working conditions. But KCTU says it wants to protect its members and other people from mad cow disease.

Hyundai's union said it is striking not only over the beef issue, but also over its stalled collective wage negotiation with management. Last year, the strike-prone union drew praise after concluding wage talks without a strike for the first time in a decade.

The walkout comes a day after U.S. beef returned to South Korean store shelves for the first time under the much-criticized beef import deal with Washington, though the sale was limited to one store run by a U.S. beef importer.

U.S. beef imports to South Korea have been largely banned since 2003, when the first case of mad cow disease was discovered in the United States. South Korea's new pro-U.S. President Lee Myung-bak agreed to lift the import ban in April just before a summit with U.S. President George W. Bush.

But the move provoked a backlash over health concerns spurred in part by false media reports about risks, along with a sense that South Korea had backed down too easily to American pressure.

As the protests peaked in June at 80,000 people, the Cabinet offered to resign and Lee reshuffled top aides. Seoul negotiated an amendment to the import deal last month to limit shipments to beef from cattle younger than 30 months, believed less susceptible to mad cow disease.

The government has vowed to get tough with the increasingly violent rallies.

In Washington, the White House announced that Bush would visit South Korea on Aug. 5-6 before heading to the Beijing Olympics. He had been expected to come to Seoul next week when he visits Japan for the G-8 summit, but that trip did not develop amid the beef protests.