Oct. 6 (Bloomberg) — Workers at BHP Billiton Ltd.’s Spence copper mine in Chile may strike as soon as Oct. 8 after a labor union rejected an increased pay offer, a union official said.

“The strike is almost imminent unless there’s a last minute miracle,” Pedro Marin, president of Chile’s Mining Federation, which represents a total of 8,500 miners in the South American country, said today in a telephone interview. BHP hasn’t increased its offer “in the way that workers hoped for,” he said.

Melbourne-based BHP, the world’s biggest mining company, requested a five-day extension to talks stipulated by Chilean law after workers in the Spence mine union rejected its previous offer. The five-day period ends tomorrow, allowing a strike to begin on Oct. 8, Marin said. Mauro Valdes, a spokesman for BHP’s Chile unit, didn’t answer calls after normal business hours.

BHP earned a record $15.4 billion in 2008. The company said Aug. 12 fiscal second-half profit declined 65 percent to $3.26 billion after the recession curbed prices and metals demand.

Copper for December delivery rose 5.75 cents, or 2.1 percent, to $2.7845 a pound on the Comex division of the New York Mercantile Exchange. The metal climbed 1.7 percent yesterday.