More than 2,000 workers remained underground for a second day Tuesday in a protest over pay and benefits at a platinum mine in South Africa.

The mine is owned by Implats, which is one of the world’s biggest platinum miners. The firm has suspended work at the Bafokeng Rasimone Platinum Mine near the city of Rustenburg, and it calls the protest illegal.

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Representatives from the National Union of Mineworkers went underground to meet with the workers but the protest "remains unresolved," Implats said.

There were no immediate details on how much the workers are paid.

More than 2,200 workers began the protest, but 167 had returned to the surface by Tuesday night, Implats said. The workers are in two shafts at the mine in North West province, about 93 miles west of the capital, Pretoria.

South Africa is by far the world’s largest platinum producer.

Such protests are not unusual. There were two recent underground protests at a gold mine in the city of Springs, near Johannesburg, in October and earlier this month. On both occasions, hundreds of workers remained underground for days amid allegations some were holding others hostage in a dispute over which union should represent them.

The Rustenburg area where the platinum mines are concentrated is the site of one of South Africa's most horrific episodes. In 2012, police killed 34 miners in a mass shooting following a prolonged strike and days of violence at another platinum mine in nearby Marikana. Six mine workers, two police officers and two private security officers were killed in the days before the shootings.