The labor union of GM Korea, the Korean unit of U.S. automaker General Motors, said Tuesday it is extending its partial strike this week as wage negotiations with the company remain deadlocked. Unionized workers again staged a four-hour walkout across all shifts from Tuesday to Wednesday, following a two-day partial strike last week, a union spokesperson said. The union is demanding a 149,600-won ($100) increase in monthly base pay, 30 million won in performance-based pay for each worker and the allocation of new vehicle production to the company's domestic plants. "The union will stage a strike if there is no progress in wage negotiations with the company on Wednesday," the spokesperson said. GM Korea exports about 410,000 vehicles manufactured at its Korean plants each year, about 85 percent of which are shipped to the United States. The company's overall vehicle sales rose 10.5 percent from a year earlier to 275,523 units in the January-June period.