Atul and Rajesh Gupta claim the attempt to bring them to stand trial for fraud and money-laundering in the Free State is politically motivated
The National Prosecuting Authority has intensified efforts to return the Guptas to South Africa
Much rests on a court decision on who owns a minority stake in the lucrative mine.
The presidency has rejected a call for a parliamentary debate on the "growing list of state deals that have benefited President Jacob Zuma’s family".
Duduzane Zuma and Indian businessmen Ajay Gupta and Jagdish Parekh told Cosatu on Tuesday they would "open their books" for the federation’s probe.