Former South African Defence Minister Mosiuoa Lekota has warned that some members of the ruling African National Congress (ANC) may leave the party.
"Today we are serving divorce papers," he said, announcing a conference in the next few weeks where a decision may be taken to split from the ANC.
Mr Lekota is a close ally of former President Thabo Mbeki who was forced to step down last month.
General elections are due in South Africa in the first half of next year.
The governing party is divided between supporters of Mr Mbeki and Jacob Zuma, who won a bitter party contest to become ANC leader last year.
Mr Lekota, known as "Terror" because of his prowess on the football field, is a former ANC chairman.
"We intend within a short period of time... to call a national convention of comrades or something of that nature to determine how to proceed to defend democracy in this country," he said, reports the AFP news agency.
"If the leadership of the ANC continues in their arrogance... we will proceed with the next step," he said.
He did not refer to Mr Zuma by name but condemned tribalism and ANC leaders who "stand on public platforms singing songs that advocate violence."
Some of Mr Zuma's supporters celebrate his Zulu origins, while his trademark song is the apartheid-era anthem "Bring Me My Machine -Gun".
Last week, Mr Lekota wrote an open letter, in which he accused the new ANC leadership of damaging democracy.
Supporters of Mr Zuma have been accused of intimidating the judiciary during his recent legal problems.
ANC Youth League leader Julius Malema has said he was prepared to kill for Mr Zuma.
Transport Minister Jeff Radebe responded by saying Mr Lekota and those who supported him were free to leave the party.
Mr Mbeki stood down after a judge suggested he may have interfered in the prosecution of Mr Zuma on corruption charges.
The former South African leader strongly denies this and has appealed against the judge's ruling.
Mr Lekota was one of several ministers who resigned along with Mr Mbeki.
Responding on Tuesday evening to rumours of a split, Mr Zuma said he thought it would be short-lived.
"I don't think it would have a very long life span, I would be surprised," he said, the South African Press Association reports.
"You can't believe in the ANC and its policies so deeply, and then form an organisation that repeats the same policies, that would be funny," he said.
The BBC's Jonah Fisher in Johannesburg says any new party would have real difficulties establishing a political foothold before next year's elections.
He says that it is unlikely that Mr Mbeki, a loyal ANC member for many years, would join any breakaway.
The BBC's Africa analyst Martin Plaut since its foundation in 1912, the ANC has shown an extraordinary degree of unity.
Where other liberation movements crumbled, it managed to stick together, despite the difficult years it spent in exile before majority rule was introduced, he says.
He says although Mr Mbeki's dismissal was the spark that ignited this rebellion, its roots are deeper.
In Mr Lekota's open letter to the party, he attacked the ANC for allowing members of the South African Communist Party (SACP) to take over leading positions.
"The ANC is not the SACP and the SACP is NOT the ANC."
The SACP is in a formal alliance with the ANC.
It was an alliance that served both well during the struggle against apartheid, when the SACP provided finances and weapons to the ANC from the Soviet Union, Mr Plaut says.
Mr Lekota argues that the distinction between the parties has now been blurred, with the ANC Secretary General Gwede Mantashe also the chairman of the SACP.
Mr Zuma's supporters accused Mr Mbeki of being too aloof and business-friendly but Mr Zuma has said he would not change South Africa's economic policies, if he does become president next year.