Rustenburg - An Association of Mineworkers and Construction Union (Amcu) official was gunned down at the Impala mine in Rustenburg on Tuesday, the union said.
"It is not for us to speculate on the motive for the killing. Whatever they are, nothing can justify the taking of another's life," union president Joseph Mathunjwa said.
"It is bad that our members are slaughtered on the mines by management's failure to ensure basic health and safety. Just two weeks ago we lost another five mine workers to the danger of going underground. Now for workers to be killed by cowardly assassins is absolutely unacceptable."
In a statement, Mathunjwa identified the official as Mpeke Nonyana, the branch treasurer at Impala mine.
Mathunjwa called on the authorities to thoroughly investigate the case and bring the perpetrators to book.
"Everyone must play their part to ensure that Mpeke Nonyana's killing is not allowed to be another unresolved murder..."
He lamented that no one has been arrested in connection with murders of Amcu members since 2012.