The National Union of Mineworkers (NUM) expressed shock on Thursday at increasing violence and intimidation at Impala Platinum and Lonmin mines.
The NUM's national executive appealed to both companies and the police to take drastic action against criminals and not allow workers to commit crimes with impunity.
"The NUM strongly warns the companies and law enforcement to not allow a situation where sooner or later we will call on our members to defend themselves in the absence of lawful intervention," it said.
It said there had been several assault cases at Lonmin and many deaths at Impala. Illegal mining, particularly in the Free State where a worker was killed, was another concern.
Mineworkers' dependants should be compensated irrespective of the cause of death, and workers should be protected, the NUM said.
It called on the Public Enterprises Minister Malusi Gigaba to intervene over the lack of a minimum service level agreement at Eskom.
This disadvantaged Eskom workers and interfered with their right to strike, the NUM said.
Its national congress takes place at Emperors Palace, in Kempton Park, from May 23 to 26.