Unionized workers at Drummond, Colombia's second-largest coal miner, have been on strike since July 23 over pay, work conditions and a demand that 400 port workers be given other jobs when automated loading is introduced in January.

In a ballot that took place last week, the minority unions on strike voted in favor of returning to work but the majority union that initiated the walkout, Sintramienergetica, said the vote was not legal and it wanted the strike to continue.

The decision rests with the ministry, which will evaluate arguments from both sides, Reuters reported.

Slightly more than half of Drummond's 5000 direct employees voted in the ballot, Drummond said.

Just more than half of those voting, about 1250, opted to end the strike.

Sintramienergetica vice president Edgar Munoz told Reuters the union was not yet ready to call a halt but would consult with its workers and the Labor Ministry to find a resolution.

"We have not contemplated lifting the strike, not under the conditions that the company wants," Munoz said.

"The vote was not legal, and we will ask that it not be recognized."

However, the fact that a majority of direct employees voted in favor of going back to work implies that some of Sintramienergetica’s 2900 members voted to end the strike.

Drummond produced 26 million tons of coal in 2012, about a third of the Andean nation’s total output.

The miner had been expected to produce 32Mt of the country’s projected 94Mt total forecast for this year. However, due to the strike the company has been forced to called a force majeure on some shipments.

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