Infighting between supporters of President Thabo Mbeki and his party deputy Jacob Zuma ahead of the Dec 16-20 ANC conference has opened the worst splits in the history of a party whose strength was long based on discipline and unity.

The Star newspaper said lawyer and ANC member Votani Majola would seek an interdict at the Johannesburg High Court on Thursday to stop the Dec 16-20 conference because "the playing fields are not level".

"We can't have a conference in this unhappy climate," Majola told the paper.

The Business Day newspaper quoted ANC Secretary-General Kgalema Motlanthe as confirming that the party was served with legal papers on Wednesday relating to charges of infringements of the bill of rights.

The paper gave no details and Motlanthe and ANC spokesman Smuts Ngonyama were not immediately reachable for comment on Thursday.

Zuma has taken a lead over Mbeki in the race for ANC chief, which would open the way for him assuming the state presidency in 2009, given the ANC's dominance of South African politics.

Investors are nervous about Zuma's close ties with the left, but on Wednesday a top aide to Mbeki told Reuters that South Africa's economic policies are unlikely to change much whoever emerges the winner. The aide also dismissed fears of instability should Zuma emerge victorious.