Facebook has been accused of making misleading claims in a dispute with New York University (NYU) researchers, by the US Federal Trade Commission (FTC).
The commission's Samuel Levine told Facebook chief Mark Zuckerberg that he was "disappointed by how your company has conducted itself in this matter".
The NYU team was studying political ads and misinformation on Facebook.
The FTC said Facebook had insinuated disabling the team members' accounts was required by an order from 2012.
However, the FTC said this was inaccurate and it supported scrutiny of targeted ads, before adding that it was pleased that Facebook had since clarified its position.
On Tuesday, Facebook blocked the accounts of the team from NYU's Cybersecurity for Democracy project.
The team's project asks people to install its Ad Observer browser extension, which then enables them to share information with researchers about the Facebook ads they see.
Cybersecurity for Democracy projects have included research into misleading political ads, right-wing misinformation and false claims about vaccines and Covid-19.
In a blog post, Facebook's product management director Mike Clark accused them of obtaining user data without consent, and violating its terms of service.
He said the company disabled their accounts, "to stop unauthorised scraping and protect people's privacy in line with our privacy program under the FTC order".
But Facebook later clarified in an interview with Wired that the existing FTC order did not force it to suspend the researchers' accounts, but merely required them to have a "comprehensive privacy programme". It said this programme is what prohibited the NYU research.
In a letter, Mr Levine told Mr Zuckerberg: "The FTC supports efforts to shed light on opaque business practices, especially around surveillance-based advertising".
The academics maintain that all they collect is data on advertisements.
Following Facebook's decision, they have attracted influential political support.
Senator Ron Wyden, chairman of the US Senate Finance Committee, accused Facebook of hypocrisy and using privacy as an "excuse to crack down on researchers exposing its problems".
Senator Mark Warner, who chairs the Senate Intelligence Committee, called the action "deeply concerning".
In the UK, Damian Collins MP, the former Digital, Culture, Media and Sport Select Committee chairman, who led its investigation into the Cambridge Analytica scandal, accused Facebook of "protecting their own interests" instead of allowing independent scrutiny of its advertising tools.
"To say that it's to protect users' data is laughable - the academic project doesn't scrape user data, it allows users to opt in and voluntarily donate information about the ads they see on Facebook," he wrote.
Mozilla, the company behind the Firefox browser, has also blogged in support of the researchers.
It said it had reviewed the code in the Ad Observer extension, adding: "It collects ads, targeting parameters and metadata associated with the ads.
"It does not collect personal posts or information about your friends. And it does not compile a user profile on its servers".