Some 400 union members at the 3,288 MW Nikola Tesla (TENT) complex which produces half of the Balkan nation's electricity, vowed to remain at the building until their demands are met. They are seeking a 26 percent wage increase based on compensation for night-shifts, which they say have not been paid since 2005. Power utility Elektroprivreda Srbije, (EPS) which runs the complex in the south-western town of Obrenovac, promised to resolve the wage row along with the government but told workers they must remain on the job to keep production going. This is especially critical, because a prolonged drought in the Balkans has pushed water levels to record lows and forced coal-fired plants to operate at maximum capacity as winter weather spurs demand. An outage of a 236 MW power plant in Bosnia earlier this week sent wholesale prices higher in the Balkans and Hungary, making production at the Tesla plant even more critical. Union representatives said they would not strike but were ready to launch a drive to donate blood, which under the law would give workers two days off. Plant officials said management tried in vain to prevent the protest and called on Serbia's energy ministry to help resolve the wage dispute. "Any radicalisation of the protest would cause a problem in the plant's operation and possibly disturbances in electricity generation," plant officials said in a statement. Serbia produces 70 percent of its electricity in coal-fired plants and the rest from hydro power. It urgently needs to upgrade its energy infrastructure, which was damaged and mismanaged during the Balkan wars of the 1990s, to meet growing demand, reduce future reliance on imports and put it in line with European Union environmental standards.