"The unions are under siege because … [of] a lack of experience amongst organisers and officials who are not equipped to deal with those challengers," Mantashe told Cosatu national office-bearers at their collective bargaining conference in Boksburg, east of Johannesburg, on Tuesday.
"Workers will begin to look for alternatives. When workers look for alternatives, they don't hear us and they don't feel us."
Mantashe told Cosatu it was divided and that there was a split in its top leadership.
"You going to actively destroy it [Cosatu]. In a year's time there will be no Cosatu … All other campaigns are going to fall flat if there is no organisation," he said.
"Build the organisation now … so you can make an impact."
Move to oust Vavi
Last week the Mail & Guardian reported that Cosatu's general secretary Zwelinzima Vavi feared not only for his political future but also his life amid reports of a move to oust him.
"I can't ignore what is happening around me," Vavi said in an open and frank discussion with the Mail & Guardian.
"There is a coordinated effort by my enemies to attack me – especially in the media. The sources that are being quoted are throwing mud in the hopes some of it will stick and are peddling lies that are simply not true."
Vavi's comments came three days after the M&G reported Vavi was being falsely accused of malfeasance by detractors within Cosatu – in the hopes that he would lose his position within the labour federation. – Sapa