Some of the workers at the Voisey's Bay nickel mine in Canada, run by Brazilian mining company Vale, began planned strike action on Saturday over work conditions, the company said on Monday.
The site, the Ovoid mine in the province of Labrador, was due to reopen on Saturday after a one-month shut-down. The firm said 120 workers, all union members, were striking.
The mine produced 77,500 tonnes of finished nickel, 55,000 tonnes of copper concentrate and some cobalt in 2008. Vale's main mining activity is in iron ore.
The workers join around 3,200 others on strike at Vale sites in Canada. Most are employed at a mine in Sudbury, Ontario, and the others are striking at the company's nickel refinery in Port Colborne, Ontario.
Vale slowed or halted operations at sites in Canada after the credit crisis worsened late last year, tipping some economies into recession and weakening demand for metals.
(Reporting by Peter Murphy)