The Association of Mineworkers and Construction Union (AMCU) says one of its members at the Lonmin mine in Wonderkop, North West, was shot and killed in front of his six-year-old daughter.
AMCU president Joseph Mathunjwa said in a statement on Saturday, Mvelisi Biyela, a health and safety office bearer at Lonmin, was gunned down outside his house on Friday.
Mathunjwa said the death of Biyela left them "shaken", but they would not be intimidated.
"Those that think their cowardice can defeat this mighty union built on the spirit of many that have paid the ultimate price, spilt their blood, left us with just their bones must think again."
Over the last months more than five leaders have been killed.
On September 12, an AMCU branch treasurer was gunned down outside the Impala Platinum mine in Rustenburg.
READ: Senior Amcu official gunned down in Rustenburg
Mathunjwa said a war had been declared against AMCU.
"We will not fight with bullets, guns and anonymous hitmen but with mass action. We will fight with a much greater weapon, the unity of AMCU, the unity of mineworkers and the unity of the working class," he said.
The trade union leader said he would not fold his arms and watch his members being killed, their wives left as widows and their children grow-up in single parent families without a father.
"Our members will not be slaughtered like flies. We will fight back and we will fight hard."
On Tuesday, AMCU is expected to hold a press conference to announce a campaign of rolling mass action.