SANTIAGO, Jul 28, 2011 (Dow Jones Commodities News via Comtex) -- Striking union workers at Chilean copper mine Escondida, controlled and operated by global miner BHP Billiton Ltd. (BHP, BHP.AU), kept production at a standstill at the world's biggest mine, a company spokeswoman said Thursday.

Workers at Escondida's sole union, representing 96% of the union-eligible labor force with 2,375 members, put down their tools late July 21 to protest what it calls unmet contract terms, forcing the mine on Wednesday to declare force majeure on its copper concentrate shipments.

Force majeure is a contract term that allows a company to temporarily halt its commitments due to an event beyond its control.

The company spokeswoman said the strike was ongoing, but she could not immediately comment on whether company representatives and the union were holding talks.

For their part, striking workers were scheduled to stage a protest in the northern port city of Antofagasta at 11 a.m. EDT.

Escondida stands to lose some 3,000 tons of copper every day workers keep production halted.

BHP holds a controlling 57.5% stake while Rio Tinto PLC (RIO, RIO.LN) holds 30%. The remaining 12.5% is held by a Japanese consortium led by Mitsubishi Corp. (MSBHY, 8058.TO).

Last year, the open-pit mine in northern Chile produced 1.086 million tons of copper, a 1% drop from its 2009 output.