They also warned that Genachowski appeared to have already made up his mind about the issue when he announced his proposal in a speech at the Brookings Institution in September.

"Your promulgating network neutrality rules seems to emanate from a fear that there may be some problems related to openness in 'the future,'" they wrote, arguing that he had provided scant evidence of actual instances of ISPs acting in way that harmed consumers. "Our view is that it is harmful for the commission to impose industry-wide rules based upon speculation about what may occur in the future."

For his part, Genachowski has pledged that the rulemaking process will be data-driven and does not assume an outcome.

The letter's signatories included John McCain, as well as several members of the Commerce Committee, the most likely venue to consider Net neutrality legislation.

Past efforts by committee members Byron Dorgan, D-N.D., and Olympia Snowe, R-Maine, to move Net neutrality legislation through the Senate have come up short, largely due to Republican opposition.

The FCC is due to consider the Net neutrality rulemaking procedure at its meeting next week.