Workers have been negotiating with the company for better pay and improved benefits since August 29, Sintraime union president Felix Herrera said according to Reuters.

Herrera said the union represented 300 workers, or about half of those directly employed by the company.

The rail line’s operation is essential for the country’s exports, with a 23-day strike by Fenoco workers last year slashing exports by almost 50%.

Herrera said the workers were seeking a 15% pay increase while the company was offering a raise equal to the annual inflation rate, which through to August was 2.27%.

"It's premature to talk about a strike," he said.

According to Colombian law, negotiations must run for 20 days, renewable if both sides wish for 20 more. Only after talks can a strike or arbitration be considered.

Workers at Alabama-based Drummond Co’s two Colombian mines and port have been on strike for 49 days over pay and potential job losses.

The Labor Ministry is deciding whether to order an end to the strike.