Internet entrepreneurs are in a panic over a Senate bill they say will censor the Web, stifle Silicon Valley startups, damage the United States' credibility on free speech and ultimately trigger the creation of an alternate-universe Internet.

The West Coast engineers say they were blindsided last Monday when the Combating Online Infringement and Counterfeits Act was introduced in the Senate Judiciary Committee. The bill has a bipartisan roster of co-sponsors who say it will be a tool for stopping the worst offenders in the world of online piracy.

The bill would give the attorney general new powers to shut down websites deemed dedicated to counterfeit material -- by going through the courts and by encouraging service providers to go after sites the Justice Department puts on a public blacklist.

According to the bill, a website would have to be "dedicated to infringing activities" to trigger the enforcement.

But Internet advocates warn the legislation would open a door for a handful of people in the federal government to wantonly power off entire websites that may be operating legally under current law. Though senators suggest the bill would save jobs by cracking down on piracy, critics say it will hurt the economy by threatening fledgling companies whenever copyrighted material shows up on their sites.

"If this bill had been law five or 10 years ago, there's a good chance that YouTube would no longer be around," Peter Eckersley, senior staff technologist at the Electronic Frontier Foundation, told FoxNews.com.

Eckersley said the bill would mark a drastic departure from current law by allowing the government not just to strip copyrighted material off an offending website, but to order the shutdown of a domain name altogether.

Eighty-seven engineers who played a role in the creation of the Internet have sent a letter to the Judiciary Committee urging it to sideline the bill.

"If enacted, this legislation will risk fragmenting the Internet's global domain name system (DNS), 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," they wrote. "All censorship schemes impact speech beyond the category they were intended to restrict, but this bill will be particularly egregious in that regard because it causes entire domains to vanish from the Web, not just infringing pages or files. Worse, an incredible range of useful, law-abiding sites can be blacklisted under this bill."

The bill's authors, co-sponsors and supporters disagree. They say it's dedicated to the worst-of-the-worst -- that the Justice Department could not shut down a site without first winning approval from a federal court and that the bill protects website operators by giving them the opportunity to remove pirating activity to get their site back online.

"No one would dispute that online infringement and counterfeiting of American intellectual property drains the American economy and costs American jobs," Senate Judiciary Committee Chairman Patrick Leahy, D-Vt., who introduced the bill, said in a written statement Wednesday. "No one would defend websites, primarily based overseas, that are dedicated to infringing activities. We continue (to) welcome input from everyone on the best way to attack the problem, but ignoring the problem, or saying it is too complicated, can no longer be an option."

The bill has broad bipartisan support on the committee, including that of Utah Republican Sen. Orrin Hatch. Thirteen of the 16 committee members are co-sponsors, giving the bill a strong chance of passing if it comes up for a vote. It was scheduled to come up for consideration Thursday,. but the chairman postponed it as the Senate prepared to adjourn until after the elections.

Critics are crying foul, saying the panel has not scheduled a hearing for the bill, but committee spokeswoman Erica Chabot noted that the panel held an oversight hearing on intellectual property enforcement in June.

"You can have hearings before you introduce a bill," she said, stressing that Leahy and the co-sponsors are continuing to talk with "stakeholders on all sides."

The biggest supporters of, and contributors to, the proposal come from the business and entertainment communities.

The AFL-CIO, which supports the bill, claims movie and music pirating costs more than 200,000 jobs. A fact sheet put out by the Senate Judiciary Committee claimed intellectual property theft, some occurring on foreign websites, costs the U.S. economy more than $100 billion annually.

Steve Tepp, a piracy expert for the U.S. Chamber of Commerce, said the censorship claims are off-base.

"This bill is a bipartisan effort that targets sites engaged in activities that all 153 countries in the WTO have agreed are illegal," he said. "These websites have no place in a legitimate online market. ... This legislation provides a critically needed tool to try to address what is globally acknowledged as criminal activity to protect America's economic interests."

The Screen Actors Guild and several other entertainment industry groups released a joint statement commending the co-sponsors and claiming the bill would be aimed at "rogue websites" dedicated to "stealing" movies and music.

Specifically, the bill would let the attorney general go through federal court to try to shut down an offending website. If the court approves, the service provider would be required to "suspend" and "lock" the domain name. Those sites would be listed on a public website. Separately, the attorney general would start another public list of offending websites that have not been ordered shut down; the Justice Department would provide immunity to any service provider that takes action against them.

Eckersley called this "outright censorship" and rattled off the names of several prominent file-sharing and file-storing sites -- RapidShare, Dropbox, MediaFire -- that could be affected. He said sites like YouTube would probably survive, but new companies similar to it could easily fall victim to the bill if it becomes law. Plus, he said, people who store files like pictures and music online could, in the stroke of a judge's pen, see those files disappear.

"It's one thing to take down an infringing file. It's another to bully an entire ecosystem of people who are trying to innovate, and that's what this bill is trying to do," he said. "The senators who are well-intentioned haven't realized how much of the astonishing economic value of the Internet they're putting at risk here."

An advocacy group that opposes the bill, Demand Progress, claims 50,000 people have signed its online petition against the bill.

"Censoring the Internet is something we'd expect from China or Iran, not the U.S. Senate," the protest petition says.

Engineers and free-speech advocates have suggested the bill would undermine efforts to press China to unlock the Internet. Plus they warn of a scenario in which engineers will circumvent the law by creating a black-market Internet where outlawed sites could be accessed.

This could create two conflicting Internet worlds, where some sites are accessible to some users and others are not; where commerce, some legitimate, happens in one world and not in the other.

"Errors and divergences will appear," the 87 engineers warned in their letter. "Contradictory addresses will confuse browsers and frustrate the people using them."

Eckersley had a simpler way to describe it: "Chaos."