A third group of workers at the Andina copper mine in central Chile went on strike on August 17, bringing the number of strikers in the sector to more than 1000, Codelco said.
Suplant union members began an indefinite strike at 8 a.m. local time after mediating and negotiating and voting to reject management's offer.
Earlier, members of the copper mine's SIIL and SUL unions went on strike on August 12 after pay negotiations failed.
Andina, 80km (50 miles) northeast of the capital, Santiago, produced 184437 metric tons of copper concentrate last year.
A union official said last week that the strike had stopped production in open-pit mines and underground operations. A spokesman for Codelco could not be reached for comment.
Codelco said in a statement that it regretted the workers' decision to continue the strike and noted that the proposal was the best offer the company could offer, given the huge investment it was making to overhaul its aging infrastructure.
Later this year, Codelco plans to commission a $1.4 billion Andina transfer project that will relocate the primary crusher plant to expand the sector's opencast mining business.
However, high copper prices this year have led unions to demand more participation in the lucrative profits of mining companies. Last month, Codelco reported first-half earnings of $3.8 billion, a tenfold increase over the same period last year. Last week, a group of workers in Caserone, Japan, also went on strike to demand higher wages.
But as a 100 per cent state-owned company, Codelco says its top priority should be to increase returns to the state to pay for public services.
