He also condemned recent pronouncements by the ANC's provincial executive committees and the South African Communist Party (SACP) over who should lead the ANC.
As expected, Cosatu this week endorsed Jacob Zuma's re-election as ANC president during the party's electoral conference in December. It also announced it would prefer Kgalema Motlanthe and Mantashe to retain their positions as deputy president and secretary general respectively.
Some in the ANC, including the youth league, want Motlanthe to replace Zuma as president and Mantashe to be replaced by Sports Minister Fikile Mbalula or national executive committee member Joel Netshitenzhe.
In an interview this week, Mantashe said ANC branches had to be given the space to nominate leaders of their choice.
"Cosatu, the SACP and the ANC provincial executive committees have no business to announce candidates for leadership positions in the ANC. They must give branches space to do that. By announcing names now, they are trying to influence the outcome of the nomination process, which is wrong," said Mantashe.
ANC provincial executive committees in Gauteng and Limpopo recently endorsed Motlanthe, whereas their counterparts in the Eastern Cape and North West announced their support for Zuma. The SACP took a resolution at its congress in July to support Zuma for a second term.
Mantashe told the Mail & Guardian he could not care less whether Cosatu had suggested his name or not. "The principle is not about the name, but respecting each other's independence.
"Both Cosatu and the SACP held their own conferences [recently]. We [the ANC] never pronounced [on] which leaders of Cosatu we wanted. Do you think we didn't have interests? We did, but the principle is not to interfere in the affairs of other alliance partners," said Mantashe.
Although Cosatu's central executive committee took a decision to endorse Zuma's leadership, it is common knowledge that not all its leaders and members support Zuma. A dominant faction in Cosatu's central executive committee, aligned to its president, Sdumo Dlamini, was lobbying hard for the federation to support Zuma's re-election, whereas the other faction aligned to general secretary Zwelinzima Vavi – who is more popular with ordinary members – was cautious in its support for the president.
Vavi, in particular, has been critical of Zuma's leadership in both the ANC and the government over the past few years. His critical stance has put him at odds with his comrades in Cosatu, who tried unsuccessfully to remove him during the federation's recent congress.
Cosatu said it would soon compose a list of potential ANC national executive committee members, drawn from its ranks, for nomination.
It also wants a political accord on key radical policy proposals with the ANC before December.
"If the alliance agreement … were to have the necessary impact, its key elements would preferably need to be agreed before December for endorsement at the Mangaung conference," Cosatu said.
"This should be a clearly spelled-out agreement, not something with vague statements of intent. It should set out a clear sequence of practical commitments to advance each of the identified areas within reasonable time frames.
"To counter growing public scepticism that radical-sounding statements are merely hollow rhetoric, it would be important to embark on a set of concrete confidence-building steps to re-establish the belief among people and the broader movement that a real change is being advanced," the federation said.
Cosatu's policy proposals include strategic nationalisation of key economic sectors of the economy, including minerals and the Reserve Bank, and the urgent introduction of comprehensive social security.