Labour union chief Felix Herrera told Reuters that Colombia’s two primary producers, Drummond and Glencore, were now bottlenecked to the tune of 130,000 tons per day after 600 employees of the transporter Fenoco had called a work stoppage last week, demanding that their union be acknowledged.

Swiss producer Glencore has not released a public statement on the matter, but Alabama-based Drummond said it was feeling the pinch.

"Coal transportation operations, by train, are paralysed due to the strike," a representative for the private company told the news service.

While a stoppage of rail transport also affects the country’s coal ports, information is not yet known about the impact of the rail strike on exports, Reuters added.

The recent safety strike by more than 8000 Drummond workers ended after four days, but Sintramienergetica union representative Joaquin Romero said the group’s wishes for enhanced safety following the recent death of worker Dagoberto Clavijo – as well as full benefits to the dead miner’s family – were not heeded.

Clavijo was fatally injured in March at Drummond’s Pribbenow surface mine in the Cesar province of northern Colombia when the truck he was operating fell into the pit.