Eight affiliates of the Congress of South African Trade Unions (Cosatu) have pledged not to participate in the federation's meetings until the National Union of Metalworkers of South Africa (Numsa) is reinstated.

The national office bearers (NOBs) of the eight affiliates said this in a joint statement on Sunday.

"The group of eight [Cosatu affiliates] has also resolved to write a letter to the African National Congress task team, which is still seeking to mediate in Cosatu, to explain very clearly that the eight unions will not participate in Cosatu meetings until Numsa is back."

Numsa was expelled from Cosatu in November for contravening Cosatu's constitution.

The expulsion was based on resolutions taken at Numsa's special congress in December 2013, including the decision not to support the African National Congress in the general elections.

Cosatu has called on Numsa to withdraw those resolutions, which it has refused to do.

An ANC task team was appointed to help the embattled Cosatu deal with internal friction, including the expulsion of Numsa.

Numsa and the eight affiliate unions' NOBs voiced their opposition to the federation continuing with its Central Executive Council (CEC) on Monday.

"We also wish to register our view that any attempt to continue with the Cosatu CEC tomorrow, as scheduled, in the absence of progress on unity issues, constitutes a destructive step which can only further deepen divisions."

The unions applauded those who picketed outside Cosatu House on Friday in opposition to Numsa's expulsion.

"This protest action is the beginning of what will become the rolling mass action in support of our programme of demands."

The national executive of Cosatu affiliate South African Democratic Teachers' Union (Sadtu), however, condemned the Friday protest.

"The NEC called on these affiliates to stop behaving like the opposition parties and spoilt brats but to use proper federation channels to raise their concerns," Sadtu general secretary Mugwena Maluleke said in a statement.

"We reject their populist rhetoric and challenge them to come to the CEC."

The Cosatu CEC had granted the request of Numsa's allies for a special national congress to consider an appeal on the expulsion of the metalworkers' union.

"They should rather prepare themselves for the special congress and stop their popstar-ism [sic] culture," Maluleke said.