Facebook has been slammed after it banned a feminist group from using an image of a plus-sized model on the grounds that it showed the body in an "undesirable manner".

Australian group Cherchez la Femme said they had posted the image for an event to celebrate the diversity of women's bodies - but were told it had breached health and safety guidelines.

Facebook has since recanted its original decision and admitted they got it wrong after they faced anger and outrage from users.

Cherchez la Femme used the image of model Tess Holliday to illustrate an event named "Feminism and fat", highlighting the movement for fat acceptance which challenges the stigma faced by plus-sized women.

But when organisers tried to promote it, they were told that the picture had been removed for promoting an "idealised physical image".

The site said such adverts were not allowed because they "make users feel bad about themselves" and suggested that they use a picture of "relevant activity" such as running or bicycling instead.

Organisers at the group said they were "raging" at the decision, in a post online.

Facebook later reinstated the picture and admitted that the original moderator had made a bad call.

"Our team processes millions of advertising images each week, and in some instances we incorrectly prohibit ads," a spokesman said.

"This image does not violate our ad policies. We apologise for the error and have let the advertiser know we are approving their ad."