Expelled ANC Youth League leader Julius Malema is a "populist, lumpen and right-wing demagogue," the Communication Workers Union said on Thursday.
"The CWU condemns the populist, lumpen and right-wing demagogue Julius Malema, who is also known as tenderpreneur," said the union in a statement.
The union accused Malema of using the recent shooting of 34 mineworkers at the Lonmin mine in Marikana for his own political gain.
"It is not exactly known when this lumpen started to be involved in the mining sector," said the union.
"The loosely-structured Malema, who suffers from a never-ending verbal diarrhoea, has been scavenging, among others, on deceased workers to gain popularity."
The union accused Malema of using the deaths to engage in attacks against President Jacob Zuma, the National Union of Mineworkers (NUM) and the Congress of SA Trade Unions.
CWU's slamming of Malema comes on the heels of comments from the National Education Health and Allied Workers' Union (Nehawu), criticising Malema and accusing him of "Nazi tactics".
Malema's spokesperson's Floyd Shivambu hit back against the unions and defended the expelled ANCYL president's stance.
"We don't respond to fools. We don't dignify fools," Shivambu said.
Shivambu accused unions critical of Malema of themselves being in factional battles, and serving the interests of Zuma.
"They're narrow, they have no politics. They're just a lackey of Jacob Zuma," Shivambu said.
Since the shooting of the 34 mineworkers a month ago, Malema has been a fixture in the Rustenburg area, speaking to disgruntled mineworkers.
This week, Malema called on mine workers to go on a nationwide strike to remove the leadership of the NUM.