SANTIAGO – Workers at Antofagasta Minerals's Zaldivar copper mine in Chile have voted in favour of strike action after rejecting a pay offer, the mine's union said on Friday.

The union said in a statement that 99% of its members had rejected a collective pay offer and a strike had been set for July 15, pending government mediation.

The union said it "regretted" the need for a strike, when the Chilean economy is in the doldrums and mining is among its primary earners, but claimed Antofagasta Minerals was attempting to strip workers' contracts of existing benefits in the latest negotiations.

The company told Reuters in a statement it would seek government-led mediation, adding: "We hope to reach an agreement through dialogue, considering the conditions of Zaldivar mine's business and its projections."

The union said the company was hiding behind a "non-existent crisis in our industry."

Major copper miners operating in Chile have largely maintained production despite economic shutdowns necessitated by the outbreak of the novel coronavirus in Chile in March.

However in recent weeks, as the virus has spread around the country and thousands of mine workers have fallen ill, miners have stepped up safety protocols, tightened shift patterns and suspended construction projects, raising fears about an - as yet unseen - impact on production.

The Zaldivar union said workers had risked their lives to maintain production at pre-pandemic levels "with a high cost to our health." Guillermo Esquivel, head of the Zaldívar union, told Reuters by phone there had been "an important number" of coronavirus cases confirmed among workers.

"We cannot accept the mine owners exploitation," it said in its statement. "If the company does not recognize our contribution and sacrifice, it will face an extensive strike that will completely stop production."

Chile’s miners, plagued by falling ore grades, were already looking to shave costs and boost efficiency before the pandemic hit. It exacerbated issues by dampening demand from China, the world’s largest copper consumer and the country first hit by the virus.

Zaldivar, which is co-owned by Barrick Gold, accounts for around 2% of Chile's annual copper production.