As Carr notes in the letter; "It is in this context that I am writing to obtain information about your work with the one specific organization - the Orwellian named NewsGuard. As exposed by the Twitter Files, NewsGuard is a for-profit company that operates as part of the broader censorship cartel. Indeed, NewsGuard bills itself as the Internet's arbiter of truth or, as its co-founder put it, a "Vaccine Against Misinformation." Newsguard purports to rate the credibility of news and information outlets and tells readers and advertisers which outlets they can trust."
Carr suggests following NewsGuard's ratings may constitute a violation of Section 230 (this is huge).