About 250 workers at the world's No. 3 copper deposit, Chile's Collahuasi mine, refused to start their morning shift on Saturday in protest over a bonus payment, union leader Manuel Munoz said.
In a statement, the company said operations have been regaining normality progressively without a great impact on production.
Collahuasi, which accounts for around 3 percent of global mined copper output, is jointly owned by global miners Xstrata and Anglo American.
Talks with company officials were planned for around 3 p.m. local time (1800 GMT), said Cristian Arancibia, another union leader.
Night-shift workers on their way out also joined the protest, meaning about a third of the mine's roughly 1,500 unionized workers were demonstrating.
The union said the protest was slowing some processing as workers blocked access to the mine, which also kept outsourced contract workers from entering.
The protest is for an indefinite period of time and it rejects the company's move to reduce the bonus payment, which goes against agreements that were reached, Arancibia said.
The company said it condemned the protest, considering that we have kept in constant contact with the union leadership, manifesting the administration's willingness to revise the bonus payment during the second half of the year.
Collahuasi produced 504,000 tons of copper in 2010, when output was hit by a month-long strike. The mine expects to produce 500,000 tons of copper this year.
Relations between the union and management have been tense over the bonus payments since last year's strike. Saturday's protest came as the union prepared to hold internal elections.
(Reporting by Fabian Cambero and Moises Avila; Writing by Hilary Burke; Editing by Paul Simao and John O'Callaghan)