The Communication Workers' Union has called for a harsh sentence for the man accused of killing UCT student Uyinene Mrwetyana to "set an example".
It has also called on Post Office managers and workers to prioritise women's safety.
The 19-year-old was raped and beaten to death with a scale inside the Clareinch post office in Cape Town late in August. A 42-year-old post office employee confessed to the crime and faces charges of murder, rape and defeating the ends of justice, News24 reported. The man in question reportedly has a previous criminal record.
The union, in a statement on Thursday, described the crime as "disgusting" and "senseless".
Call for Post Office crackdown
"We, as the majority trade union of communication workers, condemn this disgusting act ... We note that judiciary processes are underway and respect our justice system; however, we call for a harsher sentence that will set an example."
It also called for the Post Office to crack down on harassment and sexual abuse of women, saying a failure to do this could "indirectly tacitly encourag[e] many criminals instead of [letting them face] their due justice".
"We express our heartfelt condolences to the Mrwetyana family, the community of UCT and 'Nene’s' friends for the loss of their loved one. We are saying, on behalf of South African Post Office workers that, 'Not in Our Name!' … We will continue to hold accountable the workers [and management] alongside us," the union said.