A majority decision by South Africa's highest court to sentence Jacob Zuma to 15 months in jail was "judicially emotional and angry and not consistent" with the constitution, the former president's foundation said.
The Constitutional Court on Tuesday found Mr Zuma guilty of contempt for defying its order to appear at an inquiry into corruption while he was president.
It gave him five days to hand himself in to police.
In a late night statement on Wednesday, the Jacob Zuma Foundation said that Mr Zuma's lawyers would soon provide "legal advice on the options available".
The former president testified only once at the inquiry into what has become known as "state capture" but then refused to appear subsequently.
The inquiry - headed by Justice Raymond Zondo - asked the Constitutional Court to intervene.
"Our Patron has expressed his doubts about the lawfulness of the Zondo Commission, the biased manner in which it is being conducted, and the fact that it has been transformed into a 'slaughterhouse' and a forum in which all kinds of unsubstantiated and defamatory allegations have been madeagainst him," the foundation said.
BBC News
