LIMA—Workers at Peru's third-largest copper pit threw their weight behind a nationwide strike that entered its fourth day Thursday, as miners prepared to march on Congress to demand a bigger slice of corporate profits.
Global copper prices rose to near a record high on worries the strike would crimp supplies from the world's No. 2 supplier.
Workers returned to work at the Ilo smelter of Southern Copper, Peru's biggest producer, though the strike was still underway at its Cuajone mine, where the company has said output has been mostly unaffected.
The walkout is the latest sign that President Alan Garcia faces growing calls to spread the wealth from a six-year economic boom to workers and the poor, or risk losing support for his free-market policies at a time when left-wing parties are eyeing elections in 2011.
Workers at Freeport-McMoRan's Cerro Verde copper pit, Peru's third biggest, approved plans to go on strike in a final round of voting, the union said.
"On Saturday, we will go on strike, no matter what," Leoncio Amudio, the union head at Cerro Verde, told Reuters.
Laborers at Volcan's Cerro de Pasco zinc mine chose to stay at work after two rounds of votes, a union chief said on Thursday.
Workers at Newmont's Yanacocha gold mine were still deciding if they would strike, a union leader said.
Laborers were off the job at Doe Run Peru's small Cobriza copper mine, but its La Oroya smelter was operating normally, a company official has said.
Garcia's approval rating is hovering near 30 percent and his chief of staff has asked the permanent commission of Congress to vote soon on a labor bill that mining unions are pushing, while most legislators are away on recess.
As the government pleaded with Congress to approve the bill, it also declared the strike illegal, a ruling it normally makes during walkouts to persuade workers to return to work. If workers fail to return to their jobs within a week or two, the companies could fire them.
The mining unions, which were leading the march to Congress on Thursday morning, are calling for passage of the bill, which would lift caps on profit-sharing, shorten the work day, and improve retirement rules.
Failure to pass the bill could lead to more walkouts, and Peru's largest labor confederation is planning a general strike for July 9.
Since the strike started Monday, walkouts have hit some key mines but affected production only at a couple as some companies called in temporary workers.
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