Colombian coal workers voted on Saturday to strike over pay and working conditions at the 3-million-tonne-per-year La Jagua mine of Glencore's (GLEN.L) Prodeco unit, a union said.
Colombia is the world's fourth-largest coal exporter and Glencore's La Jagua - one of the mining concessions it owns in the nation - has some of the country's highest quality coal.
After 40 days of negotiations with Prodeco, laborers voted unanimously to strike after the company failed to meet their demands over pay and improved working conditions, said Ricardo Machado of the Sintraminergetica union.
Workers have 10 days to act on the strike vote but they cannot legally walk off the job for the first two days or the last two days of the period. If they do not carry out a strike during the allotted time, they must vote again.
"We were relatively close to a deal but it couldn't be reached. On Monday, we'll continue negotiating with the company," Machado told Reuters by telephone.
The discussions involved workers at Carbones de La Jagua - one of five concessions that Glencore owns in the northern Cesar province - and Prodeco.
Unions use the threat of strikes for leverage in bargaining talks with mining and oil companies, which have been returning to Colombia after a fall in guerrilla violence over the last decade due to a U.S.-backed military offensive.
Any walkout would unlikely affect prices unless it drags on for several weeks, but the industry is watching closely because the quality of coal that the mine produces is in relatively tight supply.
In 2010, laborers at La Jagua went on strike for five weeks before signing a two-year deal, and last year, they struck for eight days at the 5-million-metric tonne-per-year (5.51 million ton) Calenturitas mine.
Prodeco is Colombia's third largest coal exporter behind Drummond and Cerrejon, which is a joint venture by BHP Billiton (BLT.L), Anglo American (AAL.L) and Xstrata (XTA.L).
Prodeco produced 4.2 million metric tonnes of coal in the first quarter this year, a rise of 10 percent from the first quarter of 2011.