Nobel laureate Archbishop Desmond Tutu launched a scathing attack on the ANC, reminding its leaders they are not God, in an interview aired ahead of this month's general election.
The ANC is still respected for its long fight against white minority rule but critics say it has betrayed the struggle since coming to power in 1994.
The party is expected to win the election on April 22 but supporters are becoming increasingly disillusioned by corruption scandals.
"Let me tell this ANC government what I told the Afrikaner ... government: 'You may have power now but you are not God'," Tutu said in an interview broadcast on e.tv late on Tuesday and yesterday.
"Remember you are not God. And one day you will get your comeuppance."
The breakaway Cope could reduce the ANC's dominance in Parliament in the face of growing public anger over graft, poor services, poverty and crime.
ANC presidential candidate Jacob Zuma is awaiting word on whether corruption charges that have dogged him for years will be dropped.
South Africa's refusal to give Tibet's spiritual leader Dalai Lama a visa to attend a peace conference of Nobel laureates, including Tutu, was widely criticised. Critics accused the government of caving in to pressure from China, which it denied.
Tutu said it was an example of the moral degeneration in South Africa, which holds itself up as a model of democracy and human rights.
"I had thought that as an old man I was going to be sitting on the sidelines and watching our young people helping this new democracy flourish and grow." - Reuters