The strike at BHP Billiton's Chilean copper mine continues to unionize against alternative workers.

The union of remote operators of BHP Billiton's Escondida and Spence copper mines in Chile entered a second day of strike on Friday as the company used alternative workers to ensure continued production, union leaders said.

The 200-member union operates BHP's integrated operations center, which remotely manages mines, cathode copper and mineral processing plants in San Diego.

Union Secretary Robert Robles said union members would continue to hold demonstrations in San Diego. At the same time, the company is placing alternative workers in mines in northern Chile, a move opposed by trade unions.

The trade union has complained to the Labour Bureau that it violated the right to strike and anti-union conduct.

BHP did not respond to requests about its operations after the strike began.

The strike affects (Escondida), the world's largest copper mine, which began on Thursday after a failed attempt to sign a labour contract with the company's management added to uncertainty about global copper supplies.

The strike also marks the first strike by remote operators at the Escondida mine, testing the company's resilience to labour action in an era of more work automation or remote work.

For its part, Escondida's powerful and larger on-site workers' union has expressed support for remote workers and criticised recent labour reforms that allow companies to change workers temporarily during strikes.

"they have no right to strike effectively, which affects most Chilean workers," the union said in a statement. "

Larger unions of on-site workers will also begin collective bargaining on new contracts in the coming weeks, warning that they are preparing for a long strike.

Copper prices have soared as the world's largest economy recovers, giving unions in Chile, the world's largest copper producer, extra clout as they enter key labour negotiations.

It is still unknown when the Spence and Escondida mine strikes of BHP Billiton will end.