National Union of Metalworkers of South Africa (Numsa) general secretary Irvin Jim criticised the ANC's Gwede Mantashe and the SACP's Blade Nzimande, accusing them of dividing Cosatu, the Times reported on Tuesday.
"Him [Mantashe] and Blade are doing everything to divide Cosatu unions," he reportedly said.
Speaking at a Numsa march in Randburg on Monday, Jim said Numsa would not seek advice from ANC secretary general Mantashe and South African Communist Party general secretary Blade Nzimande on federation matters.
"No, we take our mandate direct from metalworkers. We want to tell Mantashe that we are watching his poisonous tongue."
On Tuesday, the South Gauteg High Court in Johannesburg will hear a Numsa application to have Cosatu general secretary Zwelinzima Vavi's suspension overturned.
Vavi was suspended last month on accusations of bringing Cosatu into disrepute after he admitted to having an affair with an employee. Vavi stands accused of having an affair with a subordinate.
Mantashe last week said that a "cult of personalities" created problems for Cosatu.
On Sunday, the SACP called on Jim to provide evidence of his previous claims of factionalism.
Meanwhile, Business Day reported that Vavi vowed to make 'plotters' account for their actions. Vavi says his suspension was due to a political plot to oust him.
Addressing metalworkers in Randburg, which goes against the rules of his suspension, Vavi said that those who are trying to sideline him "better go back to the drawing board." He made it clear that he was addressing the crowd as "a worker." – Additional reporting by Sapa