Johannesburg - Mineworkers at Lanxess chrome mine in Rustenburg are on an unprotected strike, the National of Union of Mineworkers said on Friday.
"Workers are demanding performance bonuses," regional co-ordinator Mxhasi Sithethi said.
Workers claimed the bonuses were approved by the company's head office in London in 2011, but never paid. The strike started on Thursday.
"The workers said a substantial amount of money is due to them. We are trying to get them back to work and [have] engaged the company on the issue. Our people went there this morning [Friday], but the gates were locked," he said.
The company was not available for comment. A security guard answered the phone, saying calls had been diverted to her guard room and no one was available on the premises.
According to the company's website it is a supplier of high quality chrome ore. It processes raw material into chrome chemical intermediates, and finally into products for, among others, working with leather.
It is situated about 14km from Rustenburg.