THE Biyagama free trade zone has been rocked by labour unrest for the second time in two weeks. In the latest incident on Monday, thousands of workers belonging to eight factories locked in their management staff after their demand for a wage increase had been turned down. The incarcerated staff included 50 South Korean nationals, according to police. At least 15 demonstrating employees were injured after riot police moved in to end the siege. The unrest began on Monday afternoon after the workers locked the factory gates and launched a sit-in protest. Executives and management staff were prevented from leaving. Police stormed the site and were compelled to fire tear-gas and baton charge the workers, who had become unruly. A bus and three cars belonging to factory executives were damaged in the clash. Among other demands put forward by the workers were the removal of the South Korean management and a reduction in working hours. The factories, which were closed yesterday, were under police guard. Last week a similar scene took place at an Australian joint-venture factory in the Biyagama investment zone. Hundreds of striking workers locked in the expatriate management of Australian joint venture Dunlop Ansell. The management team was held hostage for 36 hours while workers threatened to blow up the building if their demands for an immediate 50 per cent pay rise were not met. The factory, which employs 1,000 workers, is now closed. Twenty-six strikers have been remanded until Saturday. In a separate incident, the Colombo Commercial Fertiliser Co, in the capital's Slave Island area, was the scene of a privatisation switch-over crisis. The firm's new owners, Jayagiri Transporters, were prevented from taking physical control of the company following violent resistance by workers, police said.