Irvin Jim, head of The National Union of Metalworkers of South Africa (Numsa) says the body wants to take Cosatu to court over its central executive committee's refusal to hold a special national congress.
Jim also questioned the federation's demand for written reasons why Numsa should not be suspended or expelled from Cosatu, after Numsa announced it would not campaign for the ANC in the upcoming elections.
"We will challenge any cheap suspension of Numsa, or cheap dismissal of Numsa," said Jim, who was speaking at an event hosted by the Cape Town Press Club on Tuesday.
Nine unions petitioned the federation calling for a special national congress to deal with its internal divisions and the investigation into its suspended general secretary Zwelinzima Vavi.
The Mail & Guardian reported earlier on Tuesday that these nine pro-Vavi unions also boycotted the central executive committee meeting, and only unions affiliated to Cosatu president Sdumo Dlamini attended.
"One-third of Cosatu's affiliates had made the petition, and as per the federation's constitution, it was required to hold the special national congress," argued Jim.
"There is no longer a debate, you must go to a special congress."
If left with no option, Numsa would subject Cosatu to the courts, he said.
No vote for the ANC
Jim also suggested Numsa was being "dealt with" for not campaigning for the ruling party ahead of elections, and as such it should revisit this decision and call for members not to vote for the ANC.
"We took a very sober decision … and that decision is we will not campaign for the ANC as we used to do, that's all … We leave it to members … what political party they want to vote for," Jim said.
"Maybe we should be asking workers whether we should not revisit that discussion and basically take a decision not to vote for the ANC," he argued. "Because those that are pursuing us, they are pursuing us on the basis that we have taken a decision for allowing workers a right to choose."
Earlier on Tuesday, Cosatu's central executive committee said in a statement a special congress could not be held given the financial constraints it would place on affiliates and the full programme of other events, including election work.
The statement also expressed outrage at a number of decisions by Numsa that it said were "diametrically opposed to Cosatu policies, and go against the spirit and letter of the Cosatu constitution, principles and traditions".
These included Numsa's calls for Cosatu to break away from the alliance and its decision not to endorse or support the ANC in the elections.
In his address, however, Jim said the union could not endorse a party whose economic policies had failed to address the needs of the working class poor. Instead, Numsa leadership had been mandated to "study, research and investigate various forms of independent working class parties and to serve as a catalyst to form a party".
"Such a party would contest elections at an appropriate time."
A move to eliminate Numsa from the federation, should it happen, would not be a loss, said Jim.
"Numsa is not done a favour by being in Cosatu," he said, pointing to the "R800 000 and more" that Numsa paid Cosatu in annual dues.