The African National Congress has described Ayanda Mabulu's new artwork as "grotesque, inflammatory and of bad taste".
"No matter what message he may want to send to President Jacob Zuma and the African National Congress, we view his work as crossing the bounds of rationality to degradation, exploiting the craft of creative art for nefarious ends," the ANC's Khusela Sangoni said.
More concerning was Mabulu's abuse of the image of the late former president Nelson Mandela, the party said.
In the new painting, with a backdrop of a red and white sun ray-like design, radiating out of an ANC logo, a nude Zuma and Mandela appear to be having sex on an ornate gold and red chair.
Mandela rests his hand on his chest, with a laughing Zuma underneath him, and at first glance, Mandela appears to be comfortable. But on closer inspection, there is blood on Mandela's private parts, and a tear rolling down his cheek.
This, according to Mabulu, is a scene of rape.
The ANC said it reserved its right to seek recourse through the criminal justice system, as well as the institutions set up to promote and protect human rights.
"Such vulgarity and disdain for the dignity of others is crude, demeaning, derogatory and markedly makes the point that no freedoms, including the freedom of expression, are unlimited."
They urged South Africans to ignore Mabulu's work, after his new painting created an uproar on social media.
"Our task must be to confront and challenge delinquency, masquerading as art, that does nothing to strengthen our moral fibre or the values our society holds dear. We cannot and must not allow such crassness to be used to insult our sensibilities as a nation.
"The ANC will leave it to psychoanalysts and scholars of art to debate Mabulu's narcissistic obsession with the phallus and human genitalia in general," the party said.