Wikipedia is to shut down for 24 hours this week as part of a protest against proposed anti-piracy legislation in the US.

The English language version of the site will be unavailable from 5am (GMT) on Wednesday January 18 until 5am Thursday January 19.

The protest is in regards to anti-piracy laws currently going through congress in the US; the Stop Online Piracy Act (SOPA) and the Protect-IP Act (PIPA). If these become law, copyright holders and US Judges will have to right to shut-down websites if they believe they offer illegal access to copyrighted material such as music and movies. At present, under existing US law, a website owner must simply remove illegal content when they notified by the copyright holder. However, the new acts put the onus on the website itself to check material does not infringe copyright.

"If passed, this legislation will harm the free and open internet and bring about new tools for censorship of international websites inside the United States," the Wikimedia Foundation, which operates Wikipedia, said on its website.

Wikipedia founder Jimmy Wales used micro-blogging service Twitter to encourage web users to join the protest.

"This is going to be wow. I hope Wikipedia will melt phone systems in Washington on Wednesday. Tell everyone you know!" he said in a tweet .

"We have no indication that SOPA is fully off the table. We need to send Washington a BIG message," he added in a further tweet

Wales said around 100 million English-speaking web users would be affected by the closure of Wikipedia.

This is a first for the English version of the website, although the Italian version staged a similar protest in October over libel laws. Other websites including Reddit will join the protest. However, micro-blogging site Twitter has refused to join the protest

"Closing a global business in reaction to single-issue national politics is foolish," Twitter's CEO Dick Costolo said on the micro-blogging site, later clarifying that he was explaining why Twitter was not joining the protest rather than attacking Wikipedia's plans.

The White House has pledged to only approve parts of the bill that do not affect free speech or come across as censorship.

"Any effort to combat online piracy must guard against the risk of online censorship of lawful activity and must not inhibit innovation by our dynamic businesses large and small," the White House said.