South Africa’s top court is to rule on whether President Jacob Zuma should pay back about $23m (£15m) of state funds used to renovate his rural home.
A 2014 report by an independent watchdog said Mr Zuma had “benefited unduly” from the upgrades.
He has offered to pay some of it back but the case, brought by opposition parties, is going ahead regardless.
Large protests are expected, led by former Zuma ally turned fierce opponent Julius Malema.
The demonstration was against “corruption and cronyism” a spokesman for his Economic Freedom Fighters (EFF) said.
But Mr Zuma’s ANC party called the planned march to the court a “political exercise”.
The constitutional court in Johannesburg will also rule on whether the government flouted the law by ignoring recommendations of the watchdog, known as the Public Protector.
Mr Zuma has been cleared of wrongdoing in a police report over the Nkandla residence. The government has said the upgrades were made to boost security.
Some of the money was spent on building an amphitheatre, swimming pool, and cattle enclosure.
The saga has become a major political scandal, at one point sparking scuffles inside parliament.
It comes at a difficult time for Mr Zuma, who has also been under fire over his sacking of respected Finance Minister Nhalnhla Nene late last year.
Even though President Jacob Zuma has now offered to repay the money, the opposition Economic Freedom Fighters and Democratic Alliance insisted on pressing ahead with the case.
It is not that they do not want the president to pay; they do.
But they want to set a precedent by reinforcing the powers of the Public Protector, the corruption watchdog office set up under the country’s constitution.
Mr Zuma had justified his reluctance to repay the state by reducing Thuli Madonsela’s findings to mere recommendations and said they were not equal to orders given by a court of law.
The EFF smells blood – it hopes the Constitutional Court will conclude that the president contravened the constitution and therefore violated his oath of office.
The opposition would then no doubt demand the president’s impeachment.