WASHINGTON, (Reuters) – Popular websites Facebook,  Twitter and Craigslist threw their support behind an open  Internet framework to be unveiled by U.S. regulators this  week.  

They were among two dozen technology companies, including  Google Inc and Amazon.com Inc, which wrote a letter to the head  of the Federal Communications Commission in support of staff  proposals that would restrict network operators from favoring  certain content over others for both landlines and wireless  platforms.  

The full FCC panel is slated to vote tomorrow on whether  to issue proposals for so-called Network neutrality  

Advocates of Net neutrality say Internet services providers  must be barred from blocking or slowing traffic based on its  content, because some content could generate more revenues than  other. But providers say the increasing volume of  bandwidth-hogging services, like video sharing, requires active  management of their networks.  

“For most of the Internet’s history, FCC rules have ensured  that consumers have been able to choose the content and  services they want over their Internet connections,” they  wrote.  

“An open Internet fuels a competitive and efficient  marketplace, where consumers make the ultimate choices about  which products succeed and which fail,” they said.  

A final rule on Net neutrality is not expected until the  spring after an extensive public comment period.  

LinkedIn, EchoStar Corp, eBay Inc’s Skype and TiVo Inc also  signed the letter.  

Several Democrats and Republicans in Congress, including  the Congressional Black Caucus, have urged FCC Chairman Julius  Genachowski to proceed with caution.  

On the other hand, public interest groups such as Free  Press and Public Knowledge have urged the FCC to stand firm on  the issue, which is expected to garner the votes of the three  Democratic FCC commissioners.