Critics of the SOPA (Stop Online Piracy Act) and PIPA (PROTECT [Preventing Real Online Threats to Economic Creativity and Theft of Intellectual Property Act) legislation proposed in the US House of Representatives and Senate say it presents a serious threat to the Internet as we know it. Ostensibly designed as measures against piracy, they are regarded by some as a way to censor the Internet.

The measures provide for the withdrawal of services by domain name, payment network and advertising service providers to allegedly infringing sites. Sites located outside of the US must agree to US jurisdiction in order to present a 'counter notification' that they are not participating in the alleged violations.

Critics claim, among other things, that the proposed legislation puts too great a responsibility on the operators of sites that contain user-created content (in the event that a user links to an offending site), and that it could be used against sites hosting open-source software (particularly where the use of a particular piece of software is legal in its 'home' country but not in the US).

The latest big name to join the fight against SOPA and PIPA is Wikipedia. The English version of Wikipedia will take part in the day of action on January 18 (US time) by 'going dark' for 24 hours.

"Wikipedians from around the world have spoken about their opposition to this destructive legislation," said Jimmy Wales, founder of Wikipedia. "This is an extraordinary action for our community to take - and while we regret having to prevent the world from having access to Wikipedia for even a second, we simply cannot ignore the fact that SOPA and PIPA endanger free speech both in the United States and abroad, and set a frightening precedent of Internet censorship for the world."

The US does have a track record of persuading other governments to follow its lead, One example is the anti-circumvention provisions of Australia's Copyright Amendment Act 2006 in line with the US-Australia Free Trade Agreement.