SANTIAGO - The union at BHP Group's Escondida copper mine in Chile, the world's largest, on Wednesday urged its members to vote to strike, saying the company was attempting to impose its will and its contract offer was "insufficient".

The powerful, 2 300-member union is set to vote on BHP's contract offer between Thursday and Saturday this week.

"The Union has summoned all its members to vote en masse to reject this last offer, in order to declare a legal strike, the only tool that we have left in this scenario," the statement read.

A prolonged strike by the mine's top worker's union would constrict already tight global supplies of copper and likely send already high prices higher.

Negotiations over the last two months between the company and the union have been conducted in secrecy, against a backdrop of record high metal prices amid expectations of a gradual global recovery from the Covid-19 pandemic.

"The Company has no excuse for not responding favorably to our reasonable requests," the union said, noting the efforts of its workers during the pandemic. "The responsibility to avoid a serious conflict is entirely in the hands of ... BHP."

The union said in its statement the talks had failed to make progress on its main demands, including an improved system of professional development and performance-based compensation.

BHP said in a statement sent to Reuters that the offer "improves current conditions and incorporates new benefits in matters highly valued by workers. This was built on the basis of conversations held with the union".

If workers vote to reject the offer, further government-mediated talks of five to 10 days' duration would ensue ahead of a potential walk-out.

At Escondida, memories remain fresh of the historic 44-day stoppage in 2017 that jolted global copper markets and slowed Chile's economic growth.