Workers are striking at Petra Diamonds’ Koffiefontein mine in South Africa, adding to industrial action already taking place at two of the company’s other projects in the country.

South Africa’s National Union of Mineworkers informed the rough producer of the intention to strike from last Friday, Petra said Thursday.

  The miner is in the process of finalizing a new wage agreement for its operations in South Africa, and had warned investors earlier this month that there might be labor disruptions as a result of the negotiations.

   Strikes are also affecting underground mining at Petra’s Finsch and Kimberley operations, though plant treatment is continuing at close to normal capacity at both places, the company explained. Operations at Petra’s other South African mine, Cullinan, have escaped any impact, and production is taking place as normal.

   Petra also closed its Williamson mine in Tanzania for four days this month after national authorities seized a parcel of diamonds from the deposit over a reported valuation dispute. The company’s ability to export goods from the mine in future is unclear, it said last week.