Union workers at Chile's giant Chuquicamata copper complex, the world's second biggest, began a strike over pay early on Monday, a union leader said, a stoppage that will hit world No. 1 producer Codelco's output.

Codelco sources have estimated the Chuquicamata complex in far northern Chile, which includes the Chuquicamata and Mina Sur deposits and produces around 4 percent of the world's mined copper, will lose up to 1,800 tonnes of copper output per day and cost the state around $8 million of lost daily revenue.

The complex was expected to produce 565,000 tonnes of copper in 2009.