A court in South Africa is hearing a bid by President Jacob Zuma to block the release of a report by former anti-corruption tsar Thuli Madonsela.
She probed allegations that he let the wealthy Gupta family wield undue political influence in his government. They have denied any wrongdoing.
Mr Zuma said the report was unlawful as he had not been given a proper chance to respond to the allegations.
Meanwhile, the Nelson Mandela Foundation has called for his sacking.
In a hard-hitting statement, the foundation said Mr Zuma had “failed the test” of leadership and South Africa’s democracy as under “a real threat”.
It supported efforts to hold to account those responsible for “compromising our democratic state and looting its resources”, said the foundation, which is run by close colleagues of South Africa’s first black president who died in 2013.
Mr Zuma has been dogged by allegations of corruption for more than a decade.
He was sacked as deputy president in 2005 after his former financial adviser, Schabir Shaik, was convicted of corruption.
But four years later Mr Zuma was elected president in what was regarded as one of most remarkable political comebacks in South Africa.
Correspondents say that while the contents of Ms Madonsela’s report are unclear, Mr Zuma will be under increased pressure to resign if she reveals any adverse findings about him.
Government ministers Des van Rooyen and Mosebenzi Zwane, who have also denied being under the political influence of the Guptas, have joined the court action in support of Mr Zuma.
They are being challenged by a former MP of the governing African National Congress (ANC), Vytjie Mentor, who was a key witness in Ms Madonsela’s investigation.
She alleged in March that a member of the Gupta family had offered her the powerful public enterprise minister’s post in 2010 in exchange for business favours.
Ms Mentor also alleged that Mr Zuma was in another part of the Gupta’s family home in the upmarket Saxonworld suburb in Johannesburg when the offer was made.
Mr Zuma’s office said at the time that he had no “recollection” of Ms Mentor while the family strongly denied her allegation.
Opposition parties, including the Democratic Alliance (DA) and Economic Freedom Fighters (EFF), are also opposing Mr Zuma’s bid to block the report’s release.
EFF supporters are protesting outside the High Court in the capital, Pretoria, to demand its publication.
‘Mockery of democracy’
Mr Zuma’s court action prevented Ms Madonsela from publishing the report before she stepped down as public protector at the end of her term last month.
Her investigation was triggered by allegations by Deputy Finance Minister Mcebisi Jonas alleging that the Gupta family had made “a mockery of our hard-earned democracy” by offering him the finance minister’s post last year. He said he rejected it; the Guptas accused him of political point-scoring.
Ms Madonsela investigated Mr Zuma twice during her seven-year term.
The family, which arrived to South Africa from India in 1993, has built up holdings in mining, travel and media. It also has huge interests in computers, air travel, energy, and technology.
The son of South Africa’s president has resigned from a company owned by a family accused of wielding undue political influence in the country. In April, Mr Zuma’s son Duduzane Zuma said he was leaving his position in a mining company owned by the Guptas because of a “sustained political attack”.
The family has also said it pulling out of its businesses in South Africa.
Finance Minister Pravin Gordhan has accused the Guptas of being involved in “suspicious” financial transactions worth about $490m (£400m). The family has denied the allegation, saying it welcomed the opportunity to clear it’s name in court.
Mr Gordhan has asked a court to block the government from intervening on behalf of the family after South Africa’s biggest banks shut its accounts.
In March, South Africa’s highest court upheld Ms Madonsela’s findings that Mr Zuma “unduly benefited” from government money used to upgrade his private home in the rural area of Nkandla in KwaZulu-Natal province.
It led to widespread calls for Mr Zuma to resign, but he survived a DA-sponsored impeachment vote in parliament after ANC MPs rallied behind him.
The president is also at the centre of another case and is trying to overturn a unanimous ruling of a High Court that he should stand trial on more than 700 counts of corruption in relation to an arms deal negotiated in 1999.