Wikipedia, the online encyclopedia where users read and contribute entries, will shut its English service down for 24 hours today to oppose proposed US anti-piracy legislation.

The planned blackout is in protest at pending legislation including the Stop Online Piracy Act (SOPA) and the Protect IP Act (PIPA) in the US, according to a statement posted by Sue Gardner, executive director of the Wikimedia Foundation, the non-profit organization that operates the website.

The shutdown begins at 1 pm Beijing time. User-submitted news site Reddit, the blog Boing Boing and the Cheezburger network of comedy sites will also join the protest.

Wikipedia, available in 282 languages, contains more than 20 million articles contributed by a global volunteer community of more than 100,000 people.

In a post on Twitter, Jimmy Wales, co-founder of the crowd-sourced online encyclopedia, said he estimated that around 100 million English-speaking people will be affected by the blackout.

CNN commented that the controversial legislation has led to an all-out war between Hollywood and Silicon Valley. Media companies have united in favor of it, while tech power players are throwing their might into opposing it.

"If SOPA passes, copyright holders would be able to complain to law enforcement officials and get websites shut down. Search engines and other providers would have to block rogue sites when ordered to do so by a judge."

"Websites could also be punished for hosting pirated content in the first place, and Internet companies are worried that they could be held liable for users' actions," CNN reported.

According to Bloomberg, Internet companies, including Google and Facebook, are waging a campaign against the legislation, which they say will encourage censorship of Web content and harm technological innovation.

Gardner said the protest would go ahead despite US politicians seemingly pulling back from SOPA, after the White House stated Saturday it did not support the proposed legislation in its current form.

"All around the world, we're seeing the development of legislation intended to fight online piracy, and regulate the Internet in other ways, that hurt online freedoms," she said.

"Our concern extends beyond SOPA and PIPA: they are just part of the problem. We want the Internet to remain free and open, everywhere, for everyone."

Australian Broadcasting Corporation (ABC) quoted an analyst who uses only the name Stilgherrian as saying that companies are concerned their entire websites might be taken down by the courts.

"Once you start getting to actually identifying which parts of the site might or might not be infringing, the copyright holders have in the past tended to aim their legal action fairly broadly," Stilgherrian said.

ABC said foreign companies could also find themselves caught up by SOPA.

"If there is an Australian site holding a forum where users can post links to content, and let's say some of the content is potentially infringing, there is a chance that the Australian site could be targeted under this law," the ABC said.

Despite objections from Internet companies, Zhao Chengwei, a lawyer and director of the intellectual property division of the Yingke Law Firm, said the US act could effectively crack down on IP infringement.

"Many foreign websites, such as Youtube, have a relatively strict verification system to make sure that the material uploaded to the site does not violate copyright," he said, adding that China also has IP protection laws, but which in practice do not often favor the copyright holders.

"In China, copyright holders can notify websites containing infringing materials and ask the website to remove those materials. Search engines are also obliged to stop indexing the site as well," Zhao told the Global Times.

"But in daily practice, if the sites or search engines refuse to do so, the copyright holder must go through complex legal procedures and, if he wins the lawsuit, he could only get a small amount of compensation."

Zhao cited that under the current law, an online video site will pay a maximum of 100,000 yuan ($15,838) as compensation for running a pirated TV series.

"As a result, Chinese websites are not active in checking if their materials violate copyright laws, and copyright holders are not motivated to protect their legal interests as well," Zhao added.

Last year, Baidu, the country's top search engine, was found guilty of copyright infringement and was ordered to pay qidian.com, a popular literary website, about 550,000 yuan for infringing its copyright for five novels.

In March 2010, Qidian sued Baidu, saying its users could use the site to find links to pirated versions of five novels for which it owned the Internet copyrights.

Xu Tianran and agencies contributed to this story