Numsa will "put up a fight" if anyone tries to remove Cosatu general secretary Zwelinzima Vavi, it said on Sunday.

"We will put up a fight if there is a vote of no confidence in Vavi.... We have seen leaks and attacks against Vavi. We reject any vote of no confidence," said National Union of Metalworkers of SA (Numsa) general secretary Irvin Jim.

He said there was a clear attempt within Cosatu to undermine Vavi.

"We are witnessing a concerted attempt to undermine our efforts to deal with allegations inside the federation.

"There is a target to undermine and isolate Vavi and kill the confidence workers have in him."

Jim said Numsa's mandate to the leaders who would represent it at Cosatu's upcoming central executive committee (CEC) meeting was to reject any attempt to remove Vavi through a vote of no confidence.

Cosatu's CEC will meet from Tuesday, to address issues within the federation.

In March, the CEC called for Vavi to be investigated after allegations of alleged corruption in the acquisition of Cosatu's new headquarters.

Vavi denied the allegations and vowed to resign if they were proven to be true.

Jim said if people wanted to remove Vavi, they should do it through a congress.

"You can't sit in a room and say he [Vavi] is out.... Out from which mandate? He was elected in a congress."

Jim said Numsa would demand that the processes against Vavi be abandoned as they had been "discredited" by leaks from within Cosatu.