Workers at Cerro Verde in Peru launched a two-day pay strike on Wednesday but no effect on output was expected at the mine that produces around 2 percent of the world's copper, union and company representatives said.
The 1,100 workers started the strike after last-minute talks with the company broke down on Tuesday and they threatened to lay down their tools indefinitely on Sept. 14 if their demands for higher wages are not met.
Cerro Verde union's Secretary General William Camacho told Reuters the strike began at 7:30 a.m. local time (12:30 GMT).
But Freeport McMoRan, which has a controlling stake in the mine, said it expected output to remain unaffected.
"Cerro Verde does not anticipate that the strike will have a material impact on production," spokesman Eric Kinneberg said. "We will continue negotiating a new labor contract to replace the one that expired on August 31, 2011."
Supply worries caused by the strike, combined with a planned walk-out on Sept. 15 at Freeport's mine in Indonesia , helped push copper prices up to $9,095 per tonne from $8,8933 a tonne from Tuesday's close.
Workers at mines throughout the developing world have gone on strike in recent months, demanding a greater share of mining profits at a time of record high metal prices.
Shougang Hierro Peru, Peru's only iron producer, declared force majeure on its deliveries last week due to a continuing strike.
Cerro Verde produced 312,336 tonnes of copper in 2010. Peru is the world's No. 2 producer of copper and silver and the No. 6 gold producer. Minerals account for 60 percent of its exports.