Workers at Kia Motors Corp., an affiliate of South Korea's biggest carmaker, will resume partial strikes on Aug. 13, the first such action after they rejected a tentative agreement by union leaders.Employees will stop working for two hours in each of the day and night shifts on Aug. 13, while union representatives will hold negotiations with the company, the union said yesterday on its Web site.A majority of Kia workers on July 27 rejected a tentative pay deal for a 5.2 percent rise in base pay for this year, prolonging a dispute that has already cost the carmaker 299.7 billion won ($323 million) for 20,835 vehicles in lost production.Kia, South Korea's second-biggest automaker after its parent Hyundai Motor Co., reported a 63 percent drop in its first half net income because of lower vehicle sales.