Sintracarbon union official Orlando Cuello told Reuters that 3pm was “zero hour” for the workers at Colombia’s largest coal exporter.

Union president Igor Diaz confirmed the plans to Dow Jones Newswires, estimating 85% of the 3700 union workers placed their ballots in a strike vote that expired January 29.

Of those, 97% cast their vote in favor of a walkout demanding higher wages.

While Cerrejon has offered the group a 5% wage increase and another smaller increase in 2014, the union is demanding a 7% jump in pay in 2013 and another hike at the start of next year.

Cerrejon has not released public statement.

While Diaz said last week that the walkout could be avoided if the parties came to an agreement, negotiations were unsuccessful.

The scope of the strike could extend well beyond the 3700 union workers – some 12,000 workers, including direct employees and contractor workers, could see an impact from the strike.

Significant production, transport and fulfillment issues could also arise from the stoppage, further complicating already existing problems in the Andean nation, following an environmental inquiry into Drummond that has halted work at its shipping port.

According to Reuters, the combined loss from the stoppages could be as great as 85% of Colombia’s daily coal production.

Cerrejon is owned by Xstrata, Anglo American and BHP Billiton.

Colombia is the world’s fourth-largest coal exporter.

It produced 87 million metric tons in 2011, falling short of a 100Mt goal in part because of a 25-day coal railway strike that forced output target cutbacks.