Colombian coal miners went on strike on Thursday over pay and better working conditions at the La Jagua mining complex of Glencore's Prodeco unit, a union official said.
The walkout at La Jagua mines is unlikely to affect spot thermal coal prices in Europe or Asia unless it lasts for weeks, but many industry sources are watching whether workers from Colombia's main coal railway join La Jagua in a walkout.
"Right now everything is stopped," Ricardo Machado of the Sintraminergetica union told Reuters by telephone.
Miners at La Jagua authorized a walkout two weeks ago in Colombia, the world's fourth-largest coal exporter, after 40 days of negotiations with Prodeco failed to produce a deal.
The La Jagua complex has five mining concessions, but the negotiations were only with Carbones de La Jagua.
Machado said workers from the two other Glencore-owned mines, Carbones El Tesoro and Consorcio Minero Unido, had joined the strike, which started at 5:30 a.m. local time on Thursday.
The three areas produced 7 million tonnes of coal last year, according to mining regulator data.
Glencore was not immediately available to comment.
La Jagua's coal is the highest quality produced in Colombia and when not blended, is a niche market material, industry sources said. Glencore's Prodeco operations consist of La Jagua and Calenturitas. It has its own port facilities.
La Jagua has such a high-energy, low-sulphur coal that it often gets sold as pulverized coal for use in steelmaking.
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-tonne-per-year Calenturitas mine.
Latin America has a history of tense ties among mining companies, unions, indigenous people and environmental groups.
Unions use 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.