A group of prominent architects of the Internet added their voices Thursday to those opposing legislation in the US Congress intended to crack down on online piracy.

In an open letter to Congress, more than 80 engineers, inventors and software developers expressed concerns about the bills introduced in the Senate and the House of Representatives.

Their letter came a day after the founders of Google, Twitter, Yahoo! and other Internet giants voiced opposition to the Stop Online Piracy Act being considered in the House and the Senate version known as the Protect IP Act.

The legislation has received the backing of Hollywood, the music industry, the Business Software Alliance, the National Association of Manufacturers, the US Chamber of Commerce and other groups.

But it has come under fire from digital rights and free speech organizations for allegedly paving the way for US authorities to shut down websites accused of online piracy, including foreign sites, without due process.

"If enacted, either of these bills will create an environment of tremendous fear and uncertainty for technological innovation, and seriously harm the credibility of the United States in its role as a steward of key Internet infrastructure," the Internet architects said in their letter.

"Both bills will risk fragmenting the Internet's global domain name system and have other capricious technical consequences," they said, such as promoting censorship.

"All censorship schemes impact speech beyond the category they were intended to restrict, but these bills are particularly egregious in that regard because they cause entire domains to vanish from the Web, not just infringing pages or files," they said.

"An incredible range of useful, law-abiding sites can be blacklisted under these proposals."

The signatories, who included Vint Cerf, considered one of the "Fathers of the Internet," said censorship of Internet infrastructure "will inevitably cause network errors and security problems.

"This is true in China, Iran and other countries that censor the network today; it will be just as true of American censorship," they said.

"If the US begins to use its central position in the network for censorship that advances its political and economic agenda, the consequences will be far-reaching and destructive."