The new regulations codify the four principles set out in a 2005 Internet policy statement, which provide that Web users are entitled to access all lawful content, applications and services, and that they can attach devices to the network. The FCC also proposed codifying two additional principles -- nondiscrimination and transparency.

But there are two major ambiguities in the proposed rules, according to advocates. One is that the FCC hasn't clarified what type of activity it will consider discriminatory. The other is that the FCC carves out an exception to all rules for reasonable network management practices, yet doesn't precisely define such practices.

Five law professors sent the FCC a letter on Monday stating that those ambiguities "appear likely to provide particularly generous opportunities to try to work around the Commission's efforts." The letter was signed by Yale's Jack Balkin, South Texas College's John Blevins, University of Louisville's Jim Chen, Harvard's Larry Lessig, Stanford's Barbara van Schewick and Columbia's Tim Wu.

"We think it is surprising that the FCC would not want to provide some guidance on the applicable standard for reasonable network management, lest, as a law professor would say, the exception swallow the rule," the academics wrote.

Broadband advocacy group Free Press raised similar concerns in policy brief filed Tuesday. "Since all six principles contained in the proposed open Internet rule are subject to 'reasonable network management,' a broadly permissive exemption standard would threaten to swallow the rules," the group wrote.

The advocates also asked the FCC to clarify the type of conduct it considers "discriminatory." The notice of proposed rulemaking says that nondiscriminatory means "that a broadband Internet access service provider may not charge a content, application, or service provider for enhanced or prioritized access."

But Free Press and the law professors argue that charging for enhanced access is only one illustration of discriminatory behavior and are asking the FCC to state that other forms of discrimination would be illegal.

Marvin Ammori, a University of Nebraska law school professor who advises Free Press, tells Online Media Daily that it's important for the FCC to define its terms so the public can weigh in on the proposals.

"Ambiguities around key terms like reasonable network management make it difficult to know how strong the rules will actually be," he says.