South Africa's governing African National Congress (ANC) has been criticised for demanding a boycott of a national newspaper that reproduced a controversial painting of President Jacob Zuma.

The ANC urged "all South Africans, members of the ANC and the alliance, to indefinitely boycott buying the City Press newspaper" until it removes images of The Spear, which shows him with his genitals exposed, from its website.

The party also wants advertisers to withdraw their business. It said: "The City Press has, therefore, become a paragon of immorality, abuse and perpetrator of injustice and slander. Their refusal to remove this portrait from their website and their controlled social media is a clear indication that this newspaper does not belong to our shared democratic dispensation and values.

"This newspaper has singled itself as anti-ANC, the president, our democracy and the majority of South Africans."

Outside a court hearing in Johannesburg on Thursday, where the party was seeking to have the painting banned, the ANC national spokesman, Jackson Mthembu, whipped up a crowd of supporters by chanting: "Boycott City Press! Boycott City Press!"

Ferial Haffajee, the paper's editor-in-chief, questioned the ANC's motives, noting that pictures of The Spear are now widely available on Facebook, Twitter and Wikipedia. "The boycott call is really now more about the painting," she told South Africa's eNews channel.

Haffajee also described higher education minister Blade Nzimande's demand for a boycott of the paper as "deeply disturbing". She said: "He must be very angry and that saddens me. I am devastated by this week, by our descent into defacement and boycott over discussion and debate."

Reflecting the pressure that she and the paper are under, Haffajee tweeted: "Contrary to some opinion, I don't have balls and yes, I am hurt and scared. But, first, I'm a journalist and act in that interest."

The ANC's stand was condemned by the South African National Editors' Forum (Sanef). "While we recognise the right of the ANC to advise members on how to exercise their consumer decisions, the call for a boycott of a newspaper is tantamount to intimidation and abuse of power," it said. "This kind of behaviour is unbecoming of a party that functions in an open democratic stage and especially one which leads the national government."

But on Friday the ANC hit back, describing Sanef's remarks as "inconsistent and opportunistic". Mthembu said: "We believe that our withholding of our buying power together with all South Africans who believe that the painting is offensive, in the instance of City Press, we should demonstrate our outrage at their refusal to remove the painting on their website."