The supervisors' union voted in favor of a walk-off on July 13 after failing to agree on a new contract with Antofagasta. In Chile, however, both parties are required to participate in government-led talks, which typically last between 5 and 10 business days, before a strike can begin.
"The parties agreed to extend the mandatory mediation for one business day, so that the company can present a final proposal in response to the demands that our team has presented to them," the union said in a written statement to Reuters.
"The company has promised to deliver this new offer first thing on Monday the 27th," the union representative added.
If the two sides do not reach agreement on Monday, a strike would begin on Tuesday, he added.
Antofagasta does not comment on its labor negotiations.
Centinela produced 276,600 tonnes of copper last year.
(Reporting by Fabian Cambero, Writing by Dave Sherwood,; Editing by Louise Heavens)