Facebook is facing allegations of political censorship after a post critical of NHS privatisation which featured the story of a cancer sufferer's campaign to raise awareness by taking his protest to Downing Street was removed, raising fears its procedures are open to abuse.
Blogger Kerry-Anne Mendoza from Bristol, who runs the Scriptonite Daily blog, published an article charting the story of artist and college lecturer Mark McGowan, who is being treated for bowel cancer, and his #wheresdaddyspig journey from his treatment centre at Kings College Hospital to Downing Street.
To raise awareness of privatisation opposition, McGowan pushed a toy pig for four miles using only his nose - designed to represent pigs at the trough of the NHS - and presented a petition, signed by his children, at the door of 10 Downing Street.
Mendoza wrote an article about the event and published it on her blog, but she was taken aback after posting it on her Facebook page and being alerted by other users that Facebook began warning them that the post was spam and the content may be unsafe.
After the piece received more than 1,000 shares, all trace of it suddenly disappeared on Facebook.
"The article was removed from Facebook, from everywhere it had been shared" said Mendoza on her blog. "It was removed from every personal wall, groups and page where it had appeared. It disappeared from the wall of any user that had posted it.
"The comments and conversations underway on people's pages were erased. It was like it had never happened."
Mendoza explained that from then on anybody who tried to post the link received a pop-up from Facebook telling them that the link had been blocked for spam or unsafe content.
Another blogger, Tom Pride, claimed Facebook took the same action on his blog, except in this case he said he was made aware of a complaint coming directly from a staff member at JobCentre Plus after he posted a satirical piece in criticism of the Department of Work and Pensions.
The blogger wrote in a post published on Thursday: "Yesterday Facebook suddenly decided to flag this blog as spam - effectively censoring it by scaring away anyone who might want to link to it or share it on Facebook.
"That was obviously a surprise but I was even more surprised when a member of staff from JobCentre Plus openly boasted to me that it was she who had reported the blog to Facebook as spam after she got annoyed by this particular satirical blogpost critical of ATOS and the DWP."
The satirical blog also received more than 1,000 Facebook shares before it was flagged as spam by the social networking giant.
The blogger added: "Censoring political satire is a very dangerous game for Facebook to be playing and - even if it turns out to have been a mistake - automatically blocking links to website on the word of someone working in a government department is a real threat to freedom of expression and speech."
Mendoza said that several of her readers had complained to Facebook but had received no explanation for the incident.
"I was confused and saddened that Facebook would take this step," she told The Drum. "The blog generates lots of sharing and discussion. This article in particular raised awareness about a significant issue. For the piece to be blocked and all comments and shares related to it amounts to censorship.
"It's not only worried me but a significant number of other Facebook users who read and appreciate the blog."
At time of publication, The Drum was awaiting confirmation from Facebook on why the posts were removed and blocked from the site.
A Facebook blog post from Caroline Ghiossi in 2010, an associate on Facebook's user operations team, about Facebook's spam prevention systems said that users sometimes "misunderstand" the systems and incorrectly believe Facebook is restricting speech. It said Facebook was trying to be more transparent but could not divulge details on how its systems work.