Websites that link to pirated music and movies or sell counterfeit goods could soon be blocked in America.
US politicians are about to consider legislation which includes a raft of measures to clamp down on such sites.
The Protect IP bill gives government and copyright holders tools to stop Americans reaching illegal material.
Digital rights groups said they were "dismayed" by the proposals and feared the effect the final law would have on the internet.
"The Protect IP Act targets the most egregious actors, and is an important first step to putting a stop to online piracy and sale of counterfeit goods," said Senator Patrick Leahy in a statement released as the bill began its progress through the US legislature.
"Both law enforcement and rights holders are currently limited in the remedies available to combat websites dedicated to offering infringing content and products," said Senator Leahy, one of 10 politicians backing the proposal.
The Protect IP legislation is a re-write of the controversial Combating Online Infringement and Counterfeits Act (COICA) that narrowly failed to become law in late 2010.
The law is being opposed by the Electronic Frontier Foundation (EFF) which warned that it was no less problematic than its predecessor.
"We are no less dismayed by this most recent incarnation than we were with last year's draft," said Abigail Phillips, senior staff attorney at the EFF. She said the remedies suggested in Protect IP raised "serious First Amendment concerns about lawful expression".
Sites targeted under the Protect IP (Preventing Real Online Threats to Economic Creativity and Theft of Intellectual Property) Act would be removed from the internet's address books making them hard to find by their well-known domain name.
It allows the blocking of any domains that infringing sites switch to in order to avoid blocking. The bill also contains clauses that would force search engines to stop listing so-called infringing sites in their indexes.
As well as letting government take action, the Protect IP Act would allow copyright holders to apply for court orders to get sites blocked or de-listed.
Payment firms and ad networks could also be told to stop providing services to sites found to be infringing copyright or peddling fake goods.
Sherwin Sly, deputy legal director at the Public Knowledge digital rights group, said Protect IP threatened to unravel the consensus that the net is built upon.
If passed, it would "accelerate" the net down a path that could lead to governments everywhere sanitising online content so citizens only get what those in power think they should see, he said.