The notion of naked men marching to protest against a controversial painting of President Jacob Zuma came up at a NUM congress on Wednesday.

"Only men should march there for one reason — those men will be naked," National Union of Mineworkers (NUM) president Senzeni Zokwana told delegates in Kempton Park.

He said the painting "The Spear", depicting Zuma with exposed genitals was an "expression of how white people regard black people".

"I wonder what would have happened in Zimbabwe?" he said.

Zokwana criticised the way in which a security guard treated one of the men accused of defacing the Brett Murray painting on display at the Goodman Gallery on Tuesday.

The guard was filmed head-butting and flipping Louis Mabokela onto the floor.

"Maybe that guy was showing his master 'I can deal with blacks'," said Zokwana.

Gallery guard Paul Molesiwa (36) appeared in the Hillbrow Magistrate's Court on Wednesday for alleged assault and was granted R1000 bail.

The white man, Barend la Grange, who was arrested for defacing the painting, was treated as if he was a visitor, Zokwana said.

He said no one had the right to display such a painting.

"You can't publish pornography in the guise of artwork."

Zuma later addressed delegates, but made no reference to the artwork.

However, he did call on all South Africans to demonstrate a willingness to accept equality as a basic human right for everyone.

"You can't have some communities believing they are superior to others," he said.

"We cannot have [a] democracy of almost 20 years where we will have the problems of the past."

On Thursday, three judges of the High Court in Johannesburg will hear arguments from the ANC, Zuma and Zuma's children on why the Goodman Gallery should remove the painting and why City Press should take it off its website.

The parties will argue that this should be on the grounds that it violated Zuma and the party's dignity and rights.

City Press is opposing removing the image and the matter has been escalated to a freedom of expression issue.

In the meantime, the Goodman Gallery said it had temporarily closed its doors to the public after numerous threats.

The owner Liza Essers said she feared for safety of the gallery, its staff and visitors.