The National Union of Metalworkers of South Africa believes divisions within Cosatu are preventing radical economic change in the country.
Speaking after a special meeting of its national executive committee, Numsa said that two factions had formed within Cosatu - capitalists and socialists.
Numsa, an affiliate union of the federation, said it remained an "unashamedly socialist union."
The union has come under fire - both from Cosatu and alliance partner the ANC - for its criticism of both. They have also been a vocal supporter of suspended Cosatu general secretary Zwelinzima Vavi. They are convinced that they are being targetted
"We are convinced that the recent attacks on Numsa by senior leaders of the alliance, in the context where Cosatu is in a state of paralysis, cannot be understood outside the ongoing conflict between the working class and the capitalist class both within and outside of the alliance," said the union.
According to a report on Fin24, Numsa said that Cosatu are no longer committed to the ideals of the Freedom Charter, including strategic nationalisation.
"It is precisely this programme of action that is being frustrated through divisions within the federation. The federation will be divided until the voices that call for nationalisation are completely silenced," it said.