South African workers for the world's biggest diamond producer, De Beers, have voted to go on strike over pay.
De Beers is the latest group to be hit by strikes in South Africa
The National Union of Mineworkers (NUM) said about 11,000 of its members would down tools from 31 July to demand an 11% wage increase.
De Beers, which is 45%-owned by mining giant Anglo American, said contingency plans would be in place to operate the mines during the indefinite strike.
The planned strike is the latest union unrest that has rocked South Africa.
'Double-digits is the route'
The NUM has demanded an 11% pay offer and has said it is still open to negotiations. De Beers has offered 8%.
"Workers have told us in no uncertain terms that double-digits is the route," said Peter Bailey, the NUM's negotiator at De Beers.
De Beers told the AFP news agency: "In the event of a strike, contingency plans are in place to operate the mines.
"However, the company would prefer to settle this without disruption to its normal operations or to employees."
More than a quarter of a million engineering and metal workers walked out in protest over pay disputes earlier this month in a strike expected to bring 9,000 companies to a standstill.