On Monday Colombia's national mining and energy union, Sintramienergética, began an indefinite stoppage at Drummond's La Loma mine and shipping port.

The measure was taken because the union had not reached an agreement with the company over the workers' list of demands.

More than 2000 unionised workers at the La Loma openpit mine in the northeast of Colombia are demanding a 25% pay increase while the company offered only 7%, energy and mining union vice-president Raul Sosa told Reuters.

“All can be negotiated. We have told the company that the salary increase is the least important, because what we are interested in is job stability," Sosa said.

Reuters reported mine employees are asking for a high-risk pension scheme to cover the extreme work conditions with work days that last up to 16 hours.

They are also seeking higher pension contributions by Drummond, and retirement at 50 years of age with 10 years on the job, as well as an increase in shifts and more compensation.

The mine, which produced 22 million tons of coal last year, supplies the bulk of Colombia's 55 million ton per annum coal production.