Internet entrepreneurs are in a panic over a fast-tracking 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, which could come up for a vote as early as Thursday, 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."