Drummond and members of the Sintramienergetica union could strike on July 20, negotiator Humberto Suarez told Bloomberg, after about 3000 workers from the port and mine voted to reject the operator’s 4.5% wage increase offer.

He said union leaders would examine the company’s response before it decided whether or not to follow through with its walkoff.

“We have the votes to strike, but we are waiting to see what the company does,” he told the news service.

Sintramienergetica is seeking an 8% increase in pay.

Drummond’s most recent presentation included the 4.5% jump plus an increase of 1.25% plus inflation in the second year and inflation plus 1.5% in the third of the three-year agreement.

Should the union follow through with its strike, the stoppage could cost the Colombian government 2 billion to 3 billion pesos (between $US1.1 and $1.6 million) daily in royalties.

Suarez told Bloomberg the government officials had called for a meeting with the union, and that gathering was set for Thursday.

Drummond has not publicly commented on the issue.

The strike would be the second in just months for the Andean nation.

On February 7 workers at the Cerrejon complex walked off the job for more than a month to protest wages and benefits.

Drummond’s exports came to a halt the same month after regulators pulled the producer’s loading license temporarily following reports a barge dumped coal into the sea.