Workers at Peru's Cerro Verde mine, which accounts for about 2 percent of global copper output, started an indefinite strike for better pay and benefits on Wednesday, a union leader said.

Cerro Verde , which produced 312,336 tonnes of the red metal in 2010, is controlled by Freeport McMoran .

We've started the strike, we're meeting outside the mine, said Zenon Mujica from the Cerro Verde union.

The company was not immediately available for comment.

When workers went on strike for two days last week, the mine hired temporary workers.

Meanwhile, workers at Freeport's Grasberg mine in Indonesia, the world's No. 3 copper mine, threatened to go on strike at midnight.

The strikes could affect the price of copper, which has been volatile on concerns about waning supply. The red metal slipped to $8,740 a tonne on the London Metal Exchange from a close of $8,780 on Tuesday.

Peru is the world's No. 2 copper producer, supplying 7.7 percent of the world's output. Minerals account for about 60 percent of its exports.

Gold Copper London Copper