Bishop Mvume Dandala, an opposition candidate in the South African presidential contest, has told the BBC he would reopen a corruption case against Jacob Zuma if elected.
Zuma, the African National Congress leader, has been accused of corruption in connection with an arms deal but the case against him was recently withdrawn in what critics of the ruling African National Congress (ANC) - including former supporters who have broken away - describe as "a cover up".
ANC leaders recently accused Archbishop Emeritus Desmond Tutu, a hero of the anti-apartheid struggle, of "blasphemy" for saying he would not be happy if Mr Zuma became president.
Nelson Mandela appeared at a recent ANC rally to back the party, but effectively upstaged Zuma's "coronation", observers said.
Bishop Dandala, whose party, COPE, was founded in 2008 after former President Thabo Mbeki was ousted following a power struggle with Mr Zuma, said that all those indicted, including people from his own party, would have to face the consequences of their actions.
COPE stands for Congress of the People. Its other prominent supporters include the Rev Allan Boesak.
The Independent Electoral Commission (IEC) says that more than 23 million people, including 16,000 of the South African diaspora, have registered to vote in what is being seen as the most keenly contested election since the end of apartheid.
Voting has already started for those who are disabled, pregnant or will be temporarily out of the country on 23 April. Election officials and security force members who will be on duty on election day also go to the polls today and tomorrow.