Sintramienergetica union leader Felix Herrera told Reuters the stoppage, which included workers at Fenoco, had halted services at Glencore’s and Drummond’s coal operations.

He also confirmed no negotiations had been scheduled.

“The trains are halted,” Herrera told the news service.

“Management hasn’t called us for talks.”

The union is the second in less than a week to go on strike near coal mines in northern Colombia, South America’s largest coal supplier.

Workers at La Jagua, a mine owned by Glencore International’s Prodeco Group, went on strike on July 19, also seeking higher pay as the nation’s coal production rises.

The striking workers last week set up tents inside the mine and in a telephone interview from La Jagua, union leader Ricardo Machado said they did not have talks planned today with management.

While Reuters initially reported the mine walkout was not expected to affect European or Asian spot thermal coal prices, the statement has become a bit of an unknown variable.

Union leader Alfredo Tovar told Dow Jones Newswires that Fenoco transported about 40 million metric tonnes of export coal annually, or more than half of the country’s total shipments.

He told the news service truck transport could be used in lieu but the tonnage capabilities would likely not “even come close” to what the trains carried.

Fenoco, located in the northern state of Cesar, hauls coal for Glencore as well as Goldman Sachs’ CNR, Brazilian miner Vale and US producer Drummond.

The Cerrejon complex, equally owned by Xstrata, Anglo American and BHP Billiton, will reportedly not be affected.

Colombia is the world’s fourth largest coal exporter.

According to a recent forecast by the National Federation of Coal Producers, the South American country is expected to have 100 million tons of output in 2012, up significantly from 86Mt last year.