Unionized workers at Codelco's Chuquicamata copper mine in Chile walked off the job to protest the "unjustified layoff" of two employees, Reuters reported July 30, citing union leaders.

Labor groups including Chuquicamata Union No. 1, 2 and 3 and Antofagasta Union No. 1 agreed to down tools July 30 and blocked access to the site.

Liliana Ugarte, president of Union No. 2 at Chuquicamata, said all the unions at the mine have halted operations.

"How long the walk-off lasts depends on how negotiations go with management," Ugarte said.

Chuquicamata, which produced 330,900 tonnes of copper in 2017, has been facing union protests for months over the company's plans to transition the aging open pit operation into an underground mine.

The workers claim the company's plans to revamp the operation have failed to address their concerns. The division comprises about 5,664 employees.

Codelco struck a 27-month wage deal with the six unions at Chuquicamata in December 2016, averting the risk of a labor action.

Workers at Escondida, another copper mine in Chile, are gearing up to vote on a strike after rejecting majority-owner BHP Billiton Group's new wage offer.