Cosatu's march in Polokwane was used to slate ANC leaders in Limpopo, the party in the province said on Thursday.
Cosatu supporters refused to let a Limpopo ANC representative speak to them during their protest on Wednesday, calling him a friend of ANC Youth League leader Julius Malema.
They said they would not be spoken to by “the ANC of (premier Cassel) Mathale, and Malema, who are thieves”.
Limpopo ANC spokesman Makondelele Mathivha on Thursday said the comments were defamatory.
“This is equal to defamation of character with the full intention of not only harming his (Mathale's) good name, but also that of the ANC in the province,” he said in a statement.
“Cosatu must be careful that its honourable platforms to drive genuine causes for workers are not dragged through the mud and misused by individuals who harbour ill-intentions.”
Mathivha said the alliance partnership, between Cosatu and the ANC, must not be abused. The union federation's public platforms should be used to further the struggle of the workers.
“They must not allow themselves to be used by individuals who want to further unclear political agendas and mislead workers and the people of Limpopo. If Cosatu permits such actions to continue they run the risk of being viewed as anti-ANC.” – Sapa