THE KOREA ECONOMIC DAILY, GLOBAL EDITION

Thousands of Samsung Electronics Co. (-0.34% decrease) unionized workers in South Korea walked off job sites Monday as part of a three-day strike, pressing for higher wages and better working conditions, union leaders said.

Samsung, the world’s largest maker of memory chips and smartphones, said there were no immediate disruptions to production.

The National Samsung Electronics Union, which claims it has about 30,000 members, or nearly a quarter of the company’s workforce, said that about 6,500 workers went on strike across the nation on Monday.

Union members have been urged to down their tools for three days until Wednesday, ratcheting up pressure on management in now-stalled bargaining talks to accept their demands for higher wages, bigger bonuses and better working conditions.

“Our strike today aims to disrupt production,” a union leader said during a televised rally of striking workers near a Samsung plant in Hwaseong, south of Seoul. He warned that a bigger-scale general strike could come later this month if management fails to meet their demands.

The union in June launched what it called a first-ever walkout at Samsung, telling its members to take a day of paid leave en masse. The previous union action, however, didn’t affect operations at the company’s heavily automated chip-making facilities.

The industrial unrest at Samsung followed Friday’s rosy second-quarter earnings forecast, boosted by a continued recovery in its chip-making business. The company expects operating profit for the April-June period to see a nearly 16-fold increase compared with the same period a year earlier.

Shares are 0.5% higher, as traders largely shrugged off the union action.

Write to Kwanwoo Jun at Kwanwoo.Jun@wsj.com