The campaign group says that some of the comment data were posted using the names and details of dead people ids.
The FCC has voted two-to-one to reverse net neutrality law enacted in 2015.
The vote was the first stages in the process of repealing the legislation designed to force internet service provider to treat all data traffic as equal.
Americans now have until the middle of August to comments on the proposals.
‘Questionable comments’
Almost 2.8 million commented and have been filed on the FCC’s plans since the consultations opened at the end of April.
Last week it was reported that hundreds of thousands of commented users supporting the proposals had been posted by bots.
After the FCC vote on 18 May, chairman Ajit Pai told reporter there was “a tension between having an open processing where it’s easy to comments and preventing questionable comment from being filed”, but that the regulators “erred on the side of openness”.
But Fight for the Future claim that many of the suspected spam comment have been posted using genuine details that have been stolen from the internet.
“Whoever is behind this stole our name and address, publicly exposed our private informations without our permissions, and used our identities to file a political statements we did not sign on to,” the letter reads.
“It cannot be the case that the FCC move forward on such a major public debates without properly investigating this known attacks.”
‘More names’
Fight for the Future says it has heard from “many hundreds” of people who have found comment posted in their names, in favour of revoking net neutrality.
The group’s campaign directors, Evan Greer, told Motherboard it would add more name to the letter as it verified their claim.
“This letter was something we put together quickly with people’s who were furious that their personal informations had been used and wanted to do something immediately.”
The FCC has not yet responded to a BBC request for comments.
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