Google, Twitter and eBay say controversial Stop Online Piracy Act would give US authorities too much power over websites

Internet giants went on the attack on Wednesday, claiming legislation aimed at tackling online piracy would create an "internet blacklist bill" that would encourage censorship, kill jobs and give US authorities unrivalled powers over the world's websites.

Internet firms including Wikipedia owner Wikimedia, eBay, Google, Twitter and others protested as Congress discussed the controversial Stop Online Piracy Act (Sopa) now passing through Washington.

The act aims to tackle online piracy by giving the US Justice Department new powers to go after websites, both domestically and abroad, that host disputed copyright material. The act would allow the US to effectively pull the plug on websites and go after companies that support them technically or through payment systems. A vote on the bill could come as early as next month.

Maria Pallante, register of copyrights, told the committee: "As we all know, the internet harbours a category of bad faith actors whose very business models consist of infringing copyright in American books, software, movies, and music with impunity."

She said these "rogue" sites were the "dark side of the internet", and that while American authors, publishers, and producers had been asked to invest in online commerce, "in critical circumstances we have left them to compete with thieves."

Sopa would redress the balance she claimed by "ensuring that our law keeps pace with infringers."

She said the act would requires "all key members of the online ecosystem, including service providers, search engines, payment processors, and advertising networks, to play a role in protecting copyright interests".

Mel Watt, a North Carolina Democrat and one of the bill's sponsors, dismissed as "hyperbolic" charges the bill "will open the floodgates to government censorship." He said the comments belittled "the circumstances under which true victims of tyrannical governments actually live."

The act has powerful support from the United States Chamber of Commerce, the Motion Picture Association of America, the American Federation of Musicians, the Directors Guild of America, the Screen Actors Guild and drug companies keen for a crack down on online pharmacies undercutting US sales.

But it has met with almost universal criticism from the tech community. Mozilla, maker of the Firefox web browser, blacked out its name on its home page in an anti-Sopa protest, as did Reddit, the social news site. Tumblr launched a page attacking the act, and firms including AOL, eBay, Facebook, Google, Twitter and Zynga criticised Sopa in a full-page advertisement in The New York Times.

"We support the bills' stated goals – providing additional enforcement tools to combat foreign 'rogue' websites that are dedicated to copyright infringement or counterfeiting. Unfortunately, the bills as drafted would expose law-abiding US internet and technology companies to new and uncertain liabilities, private rights of action, and technology mandates that would require monitoring of websites," the firms wrote.

"We are concerned that these measures pose a serious risk to our industry's continued track record of innovation and job creation, as well as to our nation's cyber-security."

In a blogpost, Google said: "We strongly support the goal of the bill – cracking down on offshore websites that profit from pirated and counterfeited goods – but we're concerned the way it's currently written would threaten innovation, jobs, and free expression."

Art Bordsky, spokesman for Public Knowledge, a Washington-based public policy group, said Sopa was "the proverbial bull in the proverbial china shop" and that the bill as it stands would have "terrible consequences" for the internet.

"The international aspects alone are very worrying," he said. "It appears that the US is taking control of the entire world. The definitions written in the bill are so broad that any US consumer who uses a website overseas immediately gives the US jurisdiction the power to potentially take action against it."

At present, if Facebook, You Tube or other leading websites are found to be holding copyright material without permission, then they are told to take it down. Sopa would make it possible for the US to block the website. Such far-reaching powers could kill smaller firms and put off investors from financing new companies, said Holmes Wilson, co-founder of Fight For The Future, a lobbying group.

"Everybody uses the internet every day, these days. Everyone realises how important freedom is online. This isn't just for geeks any more," he said.

"The worst part of this bill is that the vast majority of the damage will be invisible – it will be all the companies that never start because this bill has effectively killed them."