Transport authorities in London admit they are powerless to stop a bizarre internet craze involving photographs of women eating on underground trains.
A Facebook page, entitled Women Who Eat on Tubes, seeks photographs and anecdotes of women eating while on London's underground network.
By Monday, the page had more than 16,000 members, despite claims it was just the latest example of so-called "stranger shaming" on social media.
Others have expressed concern that people posting on the website reveal further details, such as when the photograph was taken and on which line.
Some of the women appearing on the page have had their features obscured, but many others are clearly recognisable.
Responding to the furore, Steve Burton, the director of enforcement for Transport for London, said anyone who felt threatened should contact police.
"Taking photos on the Tube isn't illegal, but we ask anyone doing so to ensure that they use common sense and respect for other passengers. If someone doesn't want their photo taken, it is obviously inappropriate to do so," he said.
The people behind the page have defended the idea, saying in a statement the page "is observational not judgmental. It doesn't intimidate nor bully."
But as the page steadily gained more members on Monday, its founders did post a "code of conduct", urging anyone taking photographs for use on the site to refrain from abusive behaviour.
Sophie Wilkinson, one of the women pictured on the site, said she felt humiliated by a photograph on the site which showed her eating a takeaway salad, and the comments that accompanied it.
"Though the group information states it 'doesn't intimidate or bully', I felt victimised. And hurt," she wrote in a blog on The Debrief site.
Some commentators have expressed anger at the campaign. Feminist writer Caitlin Moran, who has almost 500,000 followers on Twitter, said she would like to turn the tables on those backing the campaign.
"This Women Eating On Tubes thing, if someone takes a picture of you, take of picture of them, and I'll tweet it," she said in a Twitter message.