Cosatu general secretary Zwelinzima Vavi is expected explain his conduct after he boycotted the trade union federation's central executive committee (CEC) meeting this week.

"The meeting expressed deep concern against the general secretary of the federation who continues to conduct himself in a manner that sought to define himself either above the organisation or to act outside the discipline of collective leadership," deputy general secretary Bheki Ntshalintshali told reporters in Johannesburg on Thursday.

He said Vavi had not attended three Congress of South African Trade Unions meetings, including this week's three-day CEC.

"It is therefore difficult for the CEC to understand why this same person would announce in the social media that he would not attend the CEC, which is his duty to prepare for," Ntshalintshali said.

"It was agreed that the general secretary must be afforded a chance in a special CEC, which will be convened soon, to have him come and explain his conduct."

On Monday Vavi tweeted that he was boycotting the meeting.

"I will not join the Cosatu CEC, I don't believe going ahead with half of the unions refusing to participate is the best way to unify," Vavi tweeted.

Responding to a tweet asking if staying away or boycotting would bring unity, Vavi said: "I twice attended the CEC with 340 000 dismissed and with half not present – that did not help unity project."

The meeting went ahead without Vavi and some Cosatu affiliate unions that had pledged not to participate until the National Union of Metalworkers of South Africa was reinstated as a member of the federation.

The unions include the Food and Allied Workers' Union; the Communication Workers' Union; and the South African Commercial, Catering, and Allied Workers' Union.

The Democratic Nursing Organisation of South Africa, which had originally said it would not attend the CEC, sent a delegation to the meeting.

Ntshalintshali said the CEC condemned those unions who did not participate.

"The CEC was clear that Cosatu had no structure which can exist parallel or outside of the constitutional structures of the federation and expect to be accorded constitutional recognition.

"We call on these affiliates to return to future meetings to engage in a democratic process where all unions are treated as equals and where all views are given equal weight," he said.