Bloggers are being asked to show their support for freedom of expression by Amnesty International.
Google has been criticised for its stance on China
The human rights group also wants web log writers to highlight the plight of fellow bloggers jailed for what they wrote in their online journals.
The organisation said fundamental rights such as free speech faced graver threats than ever before.
The campaign coincides with the start of a week-long UN-organised conference that will debate the future of the net.
"Freedom of expression online is a right, not a privilege - but it's a right that needs defending," said Steve Ballinger of Amnesty International. "We're asking bloggers worldwide to show their solidarity with web users in countries where they can face jail just for criticising the government."
Mr Ballinger said the case of Iranian blogger Kianoosh Sanjari was just one example of the dangers that some online writers can face. Mr Sanjari was arrested in early October following his blogging about conflicts between the Iranian police and the supporters of Shia cleric Ayatollah Boroujerdi.
Amnesty wanted bloggers to publicise cases such as this, said Mr Ballinger, and to declare their backing for the right to free speech online.
The human rights group is also taking its campaign to the Internet Governance Forum (IGF) - a group set up by the UN to act as a debating body for national net policies. The first big meeting of the IGF takes place in Athens from 30 October to 2 November.
"The Internet Governance Forum needs to know that the online community is concerned about free expression online and willing to stand up for it," said Mr Ballinger.
Many governments were using technology to suppress the free flow of information among their citizens, said Mr Ballinger.
"People have been locked up just for expressing their views in an email or a website," he said. "Sites and blogs have been shut down and firewalls built to prevent access to information."
Hi-tech firms such as Yahoo and Google have been criticised for the help they have given to nations such as China which works hard to monitor online discussion.
In May 2006, Amnesty International started a campaign that aimed to expose the ways that governments use the net to quash dissent. Co-ordinated via the Irrepressible.info website, the campaign asks websites to use an icon displaying text from censored sites.
Pledges gathered from those backing this campaign will be presented at the IGF.