(Recasts, adds quote and copper price) The main union at BHP...

(Recasts, adds quote and copper price)

The main union at BHP Billiton Plc's (BHP) BLT.L Escondida copper mine in Chile, the world's largest, will probably go on strike as government-mediated negotiations with the company are not progressing well, a spokesman said on Tuesday.

The two sides on Friday started a five-day government-mediated period of negotiations that effectively delays a work stoppage the Escondida Union No. 1 voted for last week. As no talks took place on Sunday, Wednesday will be the last day of the negotiations, which the union is legally required to attend, unless both parties agree to an extension.

"Three days of government mediation, and we haven't arrived at any agreement," union spokesman Carlos Allendes said. " ... It's likely that on (Thursday) the ninth, we'll have to make the strike effective on the ground, so we already have that prepared."

A strike would halt production at the mine, Allendes added. In a news release late on Monday, the union said BHP had not committed to a benefits scheme that places new and old workers on equal footing. The union, which considers equality of benefits key to any agreement, added that it tried to discuss the issue with the company, which asked to put it off to the end of negotiations.

BHP did not respond immediately to requests for comment. The possibility of a strike, which workers warn could be lengthy, has pushed up global copper prices CMCU3 in recent days. They stood at $5,833.50 per tonne at noon local time (1500 GMT), up from a morning low of $5,786 per tonne.

Escondida produced 1.15 million tonnes of copper in 2015, about 6 percent of the world's total. It is majority-controlled by BHP, with Rio Tinto (RIO) RIO.L and Japan's JECO 7768.T also holding stakes.