The UN has been criticised for stifling debate about net censorship after it disrupted a meeting of free-speech advocates in Egypt.
UN security demanded the removal of a poster promoting a book by the OpenNet Initiative (ONI) during a session at the Internet Governance Forum in Egypt.
The poster mentioned internet censorship and China's Great Firewall.
The UN has said that it had received complaints about the poster and that it had not been "pre-approved".
"If we are not allowed to discuss topics such as internet censorship, surveillance and privacy at a forum on internet governance, then what is the point of the IGF?" Ron Deibert, co-founder of the OpenNet Initiative told BBC News.
Professor Deibert said that he had been asked by the UN special rapporteur For Human Rights, who witnessed the removal, to send a formal letter of complaint.
Video of the event, posted to YouTube, show a UN security guard gathering up the poster from the floor and taking it away.
"No UN official was involved in throwing the poster on the floor," a UN spokesperson said.
"Following repeated requests from the IGF Secretariat to remove the poster from the floor, a UN Security [guard] removed it from the floor and folded it undamaged. The organisers were told that they could pick it up anytime later that evening."
The UN said they had received complaints about the poster from "delegates" and that it had not been "pre-approved for posting outside the allocated room".
Part of the banner read: "internet censorship and surveillance are increasing in democratic countries as well as authoritarian states.
"The first generation of controls, typified by China's 'Great Firewall', are being replaced by more sophisticated techniques that go beyond mere denial of information."
Mr Deibert said that he asked "repeatedly" to see "rules or regulations governing this act".
"They did not give us any, only referring to the 'objections of a member state'," he told BBC News.
It followed an earlier incident when UN officials asked the ONI to stop distributing an invitation which "mentioned Tibet", according to Mr Deibert.
The UN said the invitation was advertising "a film on 'free Tibet', which was not mentioned in the original request for the room".
"The IGF Secretariat approved the request by the OpenNet Initiative (ONI) for a room on the first day of the Forum to promote the book Access Controlled and a room was allocated for that purpose," it said in a statement.
"Officials from the Forum's Secretariat requested the organisers not to distribute the flyer or show the film as this is not what the room was requested for and second, these were concerned with a political issue not related to the Internet Governance Forum."
The ONI agreed to stop handing out the flyers, according to Mr Deibert.
Human rights activists have criticised the Internet Governance Forum for holding the meeting in Egypt. Reporters Without Borders said it was "surprised" by the decision and questioned the country's approach to free speech online.
The Internet Governance Forum (IGF) brings together government officials, businesses and net luminaries.
Web creator Sir Tim Berners-Lee used a keynote speech at the event to launch the World Wide Web Foundation, a group set up to use the web to drive social and economic change, largely in the developing world.
The IGF grew out of a previous meeting called World Summit on the Information Society that was held in Tunisia in 2005.
It has more than 1,400 participants and runs from 15 to 18 November.
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