Whoever wins is likely to succeed Mr Zuma as South African president.
Bitter leadership between the two main contenders has raised fears that the ANC could split before national elections in 2019.
On the eve of the conference, there have been three court rulings against the party, two of which have a direct bearing on the gathering.
The Pietermaritzburg High Court has granted the KwaZulu-Natal (KZN) provincial leaders leave to appeal against the September ruling, which declared the 2015 provincial elective conference unlawful, while also granting an execution order for the KZN leaders to immediately vacate office, South Africa’s Eyewitness News reports.
“In the Free State, the Bloemfontein High Court declared the provincial party’s elective conference earlier this week unlawful and it’s barred several branches from attending Saturday’s conference,” the report said.
“The North West High Court also nullified the Bojanala regional conference and set aside 32 branch general meetings, but the party says this doesn’t affect the conference.”
This therefore means that the KZN party’s provincial leaders will not be allowed to vote at the conference unless they have been sent to the gathering as ordinary branch members.
President Jacob Zuma has been in office since 2009 and shall remain head of state until those elections. South Africa limits the presidency to two five-year terms.
He has urged the party to unite behind the eventual winner in the four-day conference in Johannesburg.
The meeting takes place every five years and members have the opportunity to choose candidates for the top leadership of the party.