Unionized workers at BHP Billiton Ltd.'s (BHP) Spence copper mine in Chile received the latest wage proposal from management Wednesday and will vote on it later this week, a union spokesman said.

He declined to detail the offer as union leaders haven't yet fully gone over the proposal.

"It's very complex; it includes not only an end-of-conflict bonus as well as health, educational and other social benefits," spokesman Francisco Aravena said.

Following local labor laws, the 560 union members will vote, by a show of hands at assemblies Thursday and Friday, on whether they accept the wage offer. If rejected, a strike vote, via secret ballot, would be held Sept. 27-29, Aravena said.

Spence workers are seeking a 5.5% wage increase, social benefits and bonuses linked to international copper prices.

Before workers can go on strike, once their contracts expire, Chilean labor laws include a five-day, government-mediated negotiations period if either party calls for it. Finally, there's an additional five-day mediation period if both parties agree to it. If workers were to strike, it could only legally begin after Oct. 5. Current contracts expire Sept. 30.

The open-pit Spence mine produced about 165,000 metric tons of copper, in the form of cathodes, last year.

In addition to Spence, in Chile BHP owns the Cerro Colorado mine and controls and operates the Escondida copper mine. The latter will begin wage negotiations later this year.

Workers at several divisions of state copper giant Corporacion Nacional del Cobre, or Codelco, will also negotiate new labor contracts at the end of the year.

In 2006, when copper prices were booming, Escondida workers went on strike for nearly a month, bringing the world's largest copper mine to a standstill as they sought bigger wages and production bonuses.

A BHP representative confirmed management had presented its wage offer.

-By Carolina Pica, Dow Jones Newswires; 56-2-820-4244; carolina.pica@dowjones.com