Written by Sheena McKenzie, CNN Contributors Oscar Holland, CNN

About 100 people stripped naked in front of Facebook's New York headquarters on Sunday, as part of a protest against what they view as censorship regarding Facebook and Instagram's policies around artistic nudity.

As dawn rose over the city, the demonstrators lay naked on the road, each with large images of male nipples covering their genitalia.

The protest -- called #wethenipple -- was organized and photographed by internationally-renowned American artist Spencer Tunick and the National Coalition Against Censorship (NCAC).

Members of women's rights group Grab Them By The Ballot took part in the demonstration. The group said in a statement it was "challenging the censorship of artistic female nudity by Facebook and Instagram's 'community standards.'"

Facebook owns Instagram; CNN contacted both social media companies for comment, but had not received a reply at the time of publishing.

Naked volunteers pose for the US photographer Spencer Tunick in the ice-cold Swiss glacier of Aletsch, the largest in the Alps, as background for an environmental campaign about global warming in 2007. Credit: FABRICE COFFRINI/AFP/AFP/Getty Images

Grab Them By The Ballot's mission is to "empower women around body positivity and encourage female voter turnout in 2020," it said in a statement.

But the group's founder, Dawn Robertson, said the group has been censored by Facebook after posting artistic nude images of women.

Robertson said Facebook permanently disabled the group's ad account after it posted a nude painting with a celebratory poem for Mother's Day.

She said her personal account had also been banned six times after she posted artistic images of naked women. In correspondence seen by CNN, Facebook apologized and said it was "wrong" to have done so, but Robertson said she was later banned again.

Participants pose as part of Tunick's art installation "Return of the Nude," on July 9, 2018 in Melbourne, Australia. Credit: Michael Dodge/Getty Images AsiaPac/Getty Images

According to Instagram's community guidelines , naked images are banned on the site. "We know that there are times when people might want to share nude images that are artistic or creative in nature, but for a variety of reasons, we don't allow nudity on Instagram."

"This includes photos, videos, and some digitally-created content that show sexual intercourse, genitals, and close-ups of fully-nude buttocks. It also includes some photos of female nipples, but photos of post-mastectomy scarring and women actively breastfeeding are allowed," the policy states.

Facebook says it restricts "the display of nudity or sexual activity because some people in our community may be sensitive to this type of content."

The social media giant's community standards say: "Our nudity policies have become more nuanced over time. We understand that nudity can be shared for a variety of reasons, including as a form of protest, to raise awareness about a cause, or for educational or medical reasons. Where such intent is clear, we make allowances for the content."

Hundreds strip for mass nude photos in Melbourne

But Robertson told CNN there was little consistency in Facebook and Instagram's nudity policy. "It's like playing Russian Roulette," she said. "I never know, when I post, whether they're going to take it down."

Robertson said she accepted that not all nudity was appropriate on social media, but said Facebook's benchmark was "archaic."

"Facebook is dictating how the world views the female nude body, and they're treating it like it's a crime and it's shameful. Something has to be done. They have way more power than they should."

Controversial artist

Tunick has made his name coordinating more than 120 large-scale nude photos in public spaces around the world, most recently a photo shoot in Melbourne, Australia, involving 500 people on top of a parking lot for the city's Provocaré arts festival.

He is no stranger to controversy, having orchestrated mass nude photo shoots since the early 1990s. Some of his more unusual installations have seen him coordinate shoots in the Nevada desert and the Dead Sea.

In a video of Sunday's shoot posted on Instagram, Tunick said "there is no reason for Facebook or Instagram to censor this video or block from hashtags."

Tunick's 2010 installation The Base, took place in front of the Sydney Opera House in 2010. Credit: Spencer Tunick

In Tunick's native US, his work has proven especially controversial. The artist has been arrested on multiple occasions, and was the subject of a high-profile clash between the US Supreme Court and former New York mayor, Rudy Giuliani, who disputed his right to stage nude photo shoots in the city.

Despite legal difficulties, Tunick believes attitudes toward nudity are liberalizing around the world. In an interview with CNN earlier this year he even credited the growth of Instagram as a contributing factor.

"Nudity is part of our dialogue now -- it's not so taboo," he added. "I think that's a great thing, but at the same time, it (can still be) dangerous to be nude in public because of laws against the body in public -- for art and for nudity," he said.

Correction: This story has been corrected to clarify who organized the protest.