At least six members of the US Congress have switched sides to oppose anti-piracy legislation as protests blanketed the internet, turning Wikipedia dark and putting black slashes on Google and other sites as if they had been censored.
The legislators, including Senators Marco Rubio, Roy Blunt and John Boozman, said they were withdrawing their support, and blamed Senate Majority Leader Harry Reid for not heeding criticisms of the Senate version of the bills.
Friends of the bills, meanwhile, stepped up their efforts on Wednesday.
Creative America, a studio- and union-supported group that fights piracy, launched a television advertising campaign that it said would air in the districts of key legislators. In Times Square, it turned on a digital pro-SOPA and PIPA billboard for the day, in space provided by News Corp, which owns Fox Studios.
The group also said it is sending a team of 20 organisers to big events around the country, including the upcoming Sundance Film Festival, to try to get voters to see the situation their way.
Some volunteer editors of Wikipedia said the protest of anti-piracy legislation could threaten the credibility of their work.
"My main concern is that it puts the organisation in the role of advocacy, and that's a slippery slope," said Robert Lawton, a computer consultant and site editor who would prefer that the encyclopaedia stick to being a neutral repository of knowledge.
"Before we know it, we're blacked out because we want to save the whales."
During the 24-hour blackout, Wikipedia visitors can only see a black-and-white page which says, "Imagine a world without free knowledge", with a link to information about the controversial Stop Online Piracy Act (SOPA) and the Protect Intellectual Property Act (PIPA).
The site urges Wikipedia readers in the US to contact their local congressman to vote against the bills. "This is a quite clumsily drafted legislation which is dangerous for an open internet," Jimmy Wales, the founder of Wikipedia, said.
Google and others used the black censorship bars to draw attention to what had until recently been an obscure and technical legislative proposal to curb access to overseas websites that traffic in stolen content or counterfeit goods.
'Don't censor the web'
Ben Huh, the founder of the popular Cheezburger humour network, said on his Twitter feed that his 58 sites would also observe a blackout on Wednesday.
Search engine Google added a link to a petition against the bills on its site, reading, "Tell Congress: Please don't censor the web!".
Social media-sharing Reddit launched a 12-hour blackout, starting at 13:00 GMT.
But Dick Costollo, the chief executive of Twitter, said that while he opposed the SOPA legislation, shutting down the service was out of the question.
Rob Beschizza, Boing Boing's managing editor, speaks about the online blackout protest against SOPA
"Closing a global business in reaction to single-issue national politics is foolish," Costollo tweeted.
The bills pit technology companies such as Google and Facebook against the bill's supporters, including Hollywood studios and music labels, which say the legislation is needed to protect intellectual property and jobs.
The proposed SOPA legislation aims to crack down on online sales of pirated US movies, music or other goods by forcing internet companies to block access to foreign sites offering material that violates US copyright laws.
US advertising networks could also be required to stop online ads, and search engines would be barred from directly linking to websites found to be distributing pirated goods.
However, supporters argue the bill is unlikely to have an impact on US-based websites.
Google has repeatedly said the bill goes too far and could hurt investment.
Along with other internet companies, it has run advertisements in major newspapers urging Washington legislators to rethink its approach.
The founders of Google, Twitter, Wikipedia, Yahoo! and other internet giants said in an open letter last month the legislation would give the US government "power to censor the web using techniques similar to those used by China, Malaysia and Iran".
"We oppose these bills because there are smart, targeted ways to shut down foreign rogue websites without asking American companies to censor the internet," a Google spokesman said on Tuesday.
Source: Al Jazeera and agencies