WASHINGTON -- They predict the end of the Internet as we know it, an online world shaped by big network providers at the expense of startups and individual users.
Consumer groups and some of the world's largest technology firms are raising fears that phone and cable companies, which provide most online access, will transform the Internet by choosing which sites get the highest priority and fastest access to consumers.
The battle for "network neutrality" by opponents of the largest telecom firms has generated little policy so far.
But the fight, guided by a surprising coalition including the Gun Owners of America and the liberal MoveOn.org, has become one of the loudest technology debates in Washington with its search for guarantees that Web sites won't be blocked or impaired.
Some lawmakers are baffled by how a nebulous concern about Internet access has gained traction with little evidence that there's a problem.
"Technology moves faster than legislation," said Bartlett Cleland of the Institute for Policy Innovation, a think tank that wants less regulation. "It seems the only thing they could do is something damaging."
Big Internet names such as Google Inc., Yahoo Inc. and Amazon.com Inc. have led the fight; even Microsoft chairman Bill Gates has joined the lobbying effort.
The opposition has been led by a competing coalition of major telecom firms and trade groups that want less government involvement in the Internet.
Supporters of net neutrality say that deregulation, with court rulings and decisions by the Federal Communications Commission, has opened the door for telecom firms to wield greater control over their networks.
Several companies have hinted at their hopes of drawing additional revenue with "enhanced services."
In theory, an Internet provider could give some Web sites faster access to consumers or block competing services based on which provider is willing to pay the most. Such a move would fundamentally alter the open access that has shaped the Internet.
Consumer groups and many lawmakers say the effect would be chilling, turning away small companies and ultimately forcing consumers to pay extra online.
"There's no way you can create a toll road without creating a dirt road," said Jeannine Kenney, a senior policy analyst at Consumers Union.
"This isn't a fight between Google and Time Warner and AT&T;," she said. "This is about ultimately the higher costs that consumers are going to pay."
Proponents of network neutrality differ on what they want.
Most say that no Web sites or services should be impaired, though providers could charge more - as they do today - for a consumer to access all sites at a higher speed.
Some emergency services already get special treatment over the Internet.
And few people would object to giving priority to health care services for monitoring diabetes patients over the Internet or giving a neurosurgeon high-priority access to brain scans.
The notion of discriminating against some sites draws more concern when it comes to online entertainment, for instance, or an online phone service that a telecom company wants to prioritize over competitors.
Still, Internet providers could consider numerous approaches that wouldn't draw concerns from most consumers.
"You can't block Google, but could you block 99 percent of the Web sites without people getting upset? Sure," said Blair Levin, an analyst at Stifel Nicolaus and former chief of staff at the Federal Communications Commission.
"People tend to look at this debate in a very binary way, both morally and politically and economically," Levin said. "It's much more granular."
The debate over net neutrality has overtaken the spotlight in telecom legislation sought by phone companies to ease their entry into the pay-TV business.
The Senate Commerce Committee planned to start hearings today on its version of comprehensive telecom legislation, and net neutrality is expected to emerge as one of several contentious issues.
Rep. Edward J. Markey, a Massachusetts Democrat, introduced net neutrality legislation last week. But his bill is unlikely to proceed, considering strong Republican opposition.
When video legislation cleared the House Energy and Commerce Committee last month, members voted down an amendment to create a net neutrality policy.
Markey said leaving network providers unchecked "will stifle the ambitions of entrepreneurs all across the world" as investors consider whether startups' business plans would pass muster with big telecom firms.
Rep. Joe L. Barton, the Texas Republican who chairs the committee, maintained that companies investing billions of dollars in their networks have a right to charge fees for enhanced services.
He also highlighted the lack of clarity around the concept of net neutrality, likening it to pornography - you know it when you see it.
"I don't think all the Draconian things are going to happen that they claim will happen," Barton said.