The portrait depicting President Jacob Zuma with his genitals exposed was an assault on black culture, the Black Management Forum (BMF) said on Monday.
"The tasteless depiction of President Jacob Zuma... is not only a personal assault as well as an attack on the dignity and institutional office of the President of the Republic," the forum said in a statement.
"It is also an attack on the culture of the majority, the black people of South Africa. It cannot go unchallenged."
The painting was a "crude attempt" to reinforce the "hostility harboured by a small number of South Africans towards our democratic dispensation and towards members of the national leadership," the BMF said.
The artwork did not advance South Africa's constitutional democracy or public discourse on the topic in any way, the forum said.
It also questioned the "apparent ease" media organisations had shown in reproducing the portrait of Zuma.
The 1.85m-high painting titled "The Spear" is part of Brett Murray's "Hail to the Thief II" exhibition at the Goodman Gallery in Johannesburg. The portrait has sparked debate about freedom of expression and the right to dignity and privacy.
The African National Congress was set to argue in court on Tuesday that the painting should be removed because it violated Zuma's right to dignity and made a mockery of his office.