Around 3,500 mechanics in Colombia's key coal mining companies went on a strike on Wednesday, protesting the pay offer made to them and conditions at the mines.
The workers, employed by maintenance contractor Dimantec, put down their tools seeking an increase in wages.
If the strike continues, it is likely to affect not only the mechanical diggers and trucks that are used in open pit mines, but also the conveyor-belt loaders at the ports, Reuters reported.
Mining union Sintraime national president Felix Herrera told the news agency that Dimantec mechanics work for Colombia's biggest mining company, Cerrejon, and at sites operated by US-based Drummond and Glencore.
Employees want a raise to their regular wages and not just a one-off bonus, but this will mean that the employer will also have to pay higher social security contributions for staff.
"Dimantec has made an offer but it is below what workers want. If they can't fix the machines, the companies won't be able to work," Herrera said.
Colombia's coal sector has been facing similar disruptions since late 2012 with strikes at Cerrejon and Drummond.
In addition, a series of logistical problems last year and this have affected the country's coal exports.
A Sintraime union leader said that, if the strike continues for a long period, it will affect the country's coal output for this year, which is currently forecasted at 89.1 million tonnes.