Facebook has blocked an Australian auction house from advertising an acclaimed artist's painting depicting nude figures.
Charles Blackman's oil work Women Lovers features two nude women resting on a bed beside a cat.
Art broker Mossgreen tried to promote it on Facebook, but the social media network rejected it for "advertising adult products or services".
Mossgreen chief executive Paul Summer said the decision was "ridiculous".
"This is a very beautiful image that is not overtly sexual in any shape or form," he told the BBC.
"It's like going back to the 1950s. It's ridiculous to censor this sort of thing."
Facebook said its decision was final, although Mossgreen has since reposted images of the work.
"Such ads lead to negative user sentiment and we have zero tolerance towards such advertisements," Facebook said in a message.
Last month, a French teacher took Facebook to court after it suspended his account for posting an image of a nude woman painted by 19th Century artist Gustave Courbet.
Mr Summer said Women Lovers was expected to sell for more than A$45,000 (£28,000; $34,000) at auction next week.
"Nobody said a single thing until Facebook suddenly decided it was going to offend somebody," he said.
"I don't know who they're protecting because I have two teenage daughters myself and if I said to them that this painting has been banned I think they would have laughed at me."
Now aged 88, Blackman has been described as "the last man standing" from one of the great eras in Australian art. His contemporaries included modernist painters Arthur Boyd, Sidney Nolan and Albert Tucker.
Last year, Blackman's painting The Game of Chess was sold by Sotheby's Australia for A$1.78m.
"Charles Blackman is the most well-regarded and respected living Australian artist," Mr Summer said.