The Goodman Gallery will consult its lawyers on the classification of Brett Murray's painting "The Spear" on Friday, spokesperson Lara Koseff said.
"We felt it would have a significant impact on freedom of artistic expression. We are incredibly disappointed."
Koseff said the gallery would decide on its next step after studying the decision by the Films and Publications Board (FPB).
The FPB announced earlier that it had decided to give the painting a 16N rating. This means children under the age of 16 should not have access to the artwork, because it displays nudity.
The painting, which was vandalised at the Goodman Gallery last Tuesday, depicts President Jacob Zuma with exposed genitals.
The City Press newspaper said its legal team was also studying the ruling.
It published a photograph of the painting on its website, but removed the image on Monday, following an outcry and amid calls for a boycott.
"We are concerned about its implications for newspapers and particularly, online media," deputy editor Fikile Moyo said.
He hoped the newspaper would have more information on the implications towards the end of the weekend so it could better comment.
FPB CEO Yoliswa Makhasi said the board understood that the image of the painting had gone viral, but urged youths under the age of 16 to delete copies of it.
"We don't seek to punish people in our day-to-day work," she said.
The board said it would not report people to the police, but would work with service providers to limit access to the image.
When asked how this image differed from other nude artworks, FPB chief operations officer Mmapula Fisha said Murray's painting was not just a piece of nude art.
"The artwork has forced [our] society to revisit its painful history."
The classification had to balance this and artistic merit.
Fisha said if any of the affected parties was dissatisfied with the decision they could appeal to the FPB's appeal tribunal within 30 days.