South Africa's opposition Democratic Alliance party is challenging President Jacob Zuma's immunity from prosecution while serving office.
Democratic Alliance leader Helen Zille has taken a court case in a bid to overturn a decision to withdraw graft charges against Mr Zuma.
The president's lawyers claim he cannot be prosecuted unless he is either impeached or resigns. The charges against him were dropped in April, shortly before elections that saw Mr Zuma elected president.
State prosecutors said there had been evidence of political interference in the case under the previous government, led by Mr Zuma's rival Thabo Mbeki. Mr Zuma has always denied the charges.
In September 2008, a high court judge dismissed corruption, fraud, tax evasion and racketeering charges against Mr Zuma on a technicality, saying he should have been allowed to make representations to the National Prosecuting Authority before being officially charged.
He was first charged with corruption, racketeering and money-laundering in 2005.