Chile's SMA environmental regulator in 2016 charged SQM with overdrawing lithium-rich brine from the Salar de Atacama salt flat, prompting the company to develop a $25 million plan to bring its operations back into compliance.

The union said in a statement that the latest deal offered nothing beyond two prior proposals that were also rejected.

Lithium prices have jumped to their highest in more than three years.

Some of the biggest mining companies are expanding into or eying commodities tied to the green revolution.

The new offer values Millennial almost 7% higher at C$377 million.

Shanghai's stainless steel contract, closely watched by Chinese nickel players, hit its own life-of-contract high last month.