Workers at Peru's Cerro Verde mine, which yields 2 percent of the world's copper, agreed to end an indefinite strike they began last week, but may down tools again on Sept. 27, a union leader said Monday.

The 1,100 workers at Cerro Verde abandoned for the moment their quest for better pay and benefits as a matter of strategy, to avoid the government declaring the strike illegal, union head Leoncio Amudio said. Bruce Clements, the general manager of Cerro Verde, told Reuters in an interview last Wednesday that copper and molybdenum production had not been affected by the strike because the mine had secured temporary workers.

Cerro Verde is controlled by U.S.-based Freeport McMoRan and produced 312,336 tonnes of copper in 2010. Freeport also faces a month-long strike at its giant Grasberg mine in Indonesia, which as of Friday had delayed some 133,000 tonnes of copper ore concentrate shipments.

That raised concerns over a global shortage of the metal. The Cerro Verde union will present on Monday a new plan to strike indefinitely starting Sept. 27, Amudio told Reuters.

For us there is no more ground for dialogue, that's why we plan to resume the indefinite strike, he said. Cerro Verde and Freeport McMoRan representatives were not immediately available for comment.