A union of remote workers for BHP’s Escondida and Spence copper mines in Chile walked off the job early on Thursday after efforts to ink a labor contract deal with the company’s management fell through, fueling uncertainty over the global supply of the red metal.

The strike at Escondida, the world’s largest copper mine, and at the smaller Spence comes as copper prices have spiked amid soaring demand as the world’s largest economies revive following more than a year of coronavirus-induced stagnation.