COSATU will try to persuade Deputy President Kgalema Motlanthe not to challenge President Jacob Zuma for leadership of the ANC.
Leaders of the labour federation took the decision with just a week to go before nominations close for the party's elective conference in Mangaung next month. They fear a battle between Zuma and Motlanthe would leave the ANC deeply divided and unstable.
The Sunday Times has learnt that Cosatu's political commission, made up of 15 senior leaders from affiliate unions, took the decision in a meeting at Cosatu House on Thursday.
The meeting also resolved to exclude ANC treasurer Mathews Phosa and party deputy secretary-general Thandi Modise from a list of national executive committee (NEC) members who Cosatu wants to lead the ANC.
Two senior Cosatu leaders who attended the meeting said the organisation believed a decision by Motlanthe to stay out of the leadership race would help to ease tensions between supporters of the two leaders.
"We are going to approach Kgalema on the principle of stability and unity," a union official said on condition of anonymity.
"Kgalema carries a lot of weight on this issue of Mangaung. He is the one man who is giving us a lot of stress."
Cosatu last month resolved to back Zuma's bid for a second term and called for the removal of Modise and Phosa, who it accused of contradicting the party line in public.
This followed a plea from the labour federation, which avoided a leadership battle at its congress in September, for the ANC to follow its example.
Motlanthe has also been under pressure from the Umkhonto we Sizwe Military Veterans Association not to take on Zuma.
The Cosatu official warned that if Motlanthe went ahead and challenged Zuma, Cosatu would not support him.
"If Kgalema contests, there will be consequences. He will be left out after Mangaung.
"Kgalema holds a lot of power on this matter of Mangaung. If he decides not to contest, then Mangaung will not be full of fights," the official said.
Another Cosatu leader who attended the political commission said the meeting had wanted to check progress on the federation's efforts to persuade Motlanthe.
"This [decision to approach Motlanthe] was a central executive committee decision. The political commission was checking on progress on the decision to approach Motlanthe," he said.
Referring to Phosa and Modise, this union leader said: "Thandi and Phosa are not in. We are not discussing those two. They have failed to unite the top six. They have been speaking against the decisions of the ANC."
However, the Cosatu leaders acknowledged that it would be hard to leave anti-Zuma figures like Sports Minister Fikile Mbalula out of the ANC NEC.
"You can't leave him out of the NEC," one of them said.
Cosatu spokesman Patrick Craven refused to comment on the matter.
Motlanthe's spokesman Thabo Masebe could not be drawn on Cosatu's decision, saying he was not aware of it.
"I don't think it will help to speculate what they will say. Ask them. The deputy president has nothing to say."