The bill would slap a 3% royalty on sales of copper that would increase sharply alongside rising prices.

“Fundamentals remain intact and there will be growing copper demand ahead," Codelco chairman Juan Benavides said.

Peru's southern Andean region has large mines such as MMG's Las Bambas and Grupo Mexico's Los Chancas.

Union leader said BHP had used the regulatory issues it faces as an excuse to lowball workers with an inadequate contract proposal.

The metal has surged 32% this year, second only to tin among the six base metals traded on the LME.

The 36-month deal does not provide a pay increase but includes a signing bonus equivalent to about $6,500 per member, plus incentives.

SQM shareholder Julio Ponce said the object of the share sale was "to strengthen the capital structure" of the company.

In an unprecedented year marked by disruptions due to the global pandemic, copper mine production was contingent on how each company overcame operational challenges.