By Fabian Cambero
ANTOFAGASTA, Chile (Reuters) - Workers at BHP Billiton's (AX:BHP) (L:BLT) Escondida in Chile, the world's biggest copper mine, walked off the job on Thursday, their union said, marking the start of a strike that threatens to disrupt the international supply of the widely used industrial metal.
It said no miners arrived for morning work aboard buses which normally deliver them to the vast deposit, which accounted for about 6 percent of global production in 2015.
"The buses are empty, there are no workers in them to replace the night shift," union spokesman Carlos Allendes told Reuters. "The strike is now in effect."
The union has warned that it is prepared for a lengthy strike.
At a camp near the mine, protesting workers settled in for the long haul, equipped with stockpiles of gas cylinders, portable cookers and tents to weather the Chilean high desert's scorching sun and frigid nights.
Escondida's processing plants, which had begun going offline on Wednesday, are now completely stopped, the union added.
Striking workers also blocked roads at the Coloso port, where hundreds of thousands of tonnes of copper are shipped annually.
"We are united and strong to make sure this is a success considering the measures the company has taken against its workers," said Claudio Perez, plant worker at the Coloso port.
BHP Billiton spokesmen were not immediately available for comment.
BHP has said it would halt production during the strike because it could not guarantee the safety of the 80 workers the government had authorized to perform critical duties, such as equipment upkeep and adhering to environmental protocols.
Only a handful of workers remained at the mine and port performing critical duties on Thursday morning, union director Jaime Thenoux said.
The strike at Escondida follows weeks of fractious labour negotiations, as both sides were unable to agree on a new salary and benefits scheme, sending copper prices higher.
Copper prices eased on Thursday as some investors cashed in the previous day's gains, though it remained underpinned by the threat of supply disruptions.
Among other things, the union complained that BHP had not committed to placing new and longtime workers on equal footing in terms of benefits, something it considers essential to any agreement.
Escondida is majority-controlled by BHP, with Rio Tinto (AX:RIO) (L:RIO) and Japan's JECO (T:7768) also holding stakes.