AUSTRALIA will join China in implementing mandatory censoring of the internet under plans put forward by the Federal Government.

The revelations emerge as US tech giants Google, Microsoft and Yahoo, and a coalition of human rights and other groups unveiled a code of conduct aimed at safeguarding online freedom of speech and privacy.

The government has declared it will not let internet users opt out of the proposed national internet filter.

The plan was first created as a way to combat child pronography and adult content, but could be extended to include controversial websites on euthanasia or anorexia.

Communications minister Stephen Conroy revealed the mandatory censorship to the Senate estimates committee as the Global Network Initiative, bringing together leading companies, human rights organisations, academics and investors, committed the technology firms to "protect the freedom of expression and privacy rights of their users".

Mr Conroy said trials were yet to be carried out, but "we are talking about mandatory blocking, where possible, of illegal material."

The net nanny proposal was originally going to allow Australians who wanted uncensored access to the web the option of contacting their internet service provider to be excluded from the service.

Human Rights Watch has condemned internet censorship, and argued to the US Senate "there is a real danger of a Virtual Curtain dividing the internet, much as the Iron Curtain did during the Cold War, because some governments fear the potential of the internet, (and) want to control it"

Groups including the System Administrators Guild of Australia and Electronic Frontiers Australia have attacked the proposal, saying it would unfairly restrict Australians' access to the web, slow internet speeds and raise the price of internet access.

EFA board member Colin Jacobs said it would have little effect on illegal internet content, including child pornography, as it would not cover file-sharing networks.

"If the Government would actually come out and say we're only targeting child pornography it would be a different debate," he said.

The technology companies' move, which follows criticism that the companies were assisting censorship of the internet in nations such as China, requires them to narrowly interpret government requests for information or censorship and to fight to minimise cooperation.

The initiative provides a systematic approach to "work together in resisting efforts by governments that seek to enlist companies in acts of censorship and surveillance that violate international standards", the participants said.

In a statement, Yahoo co-founder and chief executive Jerry Yang welcomed the new code of conduct.

"These principles provide a valuable roadmap for companies like Yahoo operating in markets where freedom of expression and privacy are unfairly restricted," he said.

"Yahoo was founded on the belief that promoting access to information can enrich people's lives, and the principles we unveil today reflect our determination that our actions match our values around the world."

Yahoo was thrust into the forefront of the online rights issue after the Californian company helped Chinese police identify cyber dissidents whose supposed crime was expressing their views online.

China exercises strict control over the internet, blocking sites linked to Chinese dissidents, the outlawed Falun Gong spiritual movement, the Tibetan government-in-exile and those with information on the 1989 Tiananmen massacre.

A number of US companies, including Microsoft, Cisco, Google and Yahoo, have been hauled before the US Congress in recent years and accused of complicity in building the "Great Firewall of China".

The Australian Christian Lobby, however, has welcomed the proposals.

Managing director Jim Wallace said the measures were needed.

"The need to prevent access to illegal hard-core material and child pornography must be placed above the industry's desire for unfettered access," Mr Wallace said.