South Africa's National Union of Mineworkers (NUM) said on Monday its members had downed tools at the Koornfontein coal mine operated by Glencore in a dispute over pay.
The NUM said in a statement the strike began on Friday after talks brokered by a government mediator were deadlocked.
NUM regional secretary Stanley Lebello said around 600 of the union's members were taking part in the strike, which he said was triggered by a dispute over the structuring of packages for employees who face lay offs.
He said the union was also seeking permission to launch protest strikes at other Glencore operations.
Officials from Glencore could not immediately be reached for comment.
Reporting by Ed Stoddard