A non-profit that monitors online hate speech and disinformation, the Center for Countering Digital Hate (CCDH) says that Elon Musk’s lawyers sent CEO Irman Ahmed a threatening legal letter over a CCDH article which said that Twitter fails to act on 99% of Twitter Blue accounts’ hateful tweets.

In a copy of the letter that the CCDH posted, Musk’s lawyer Alex Spiro critiques the CCDH’s methodology, in which CCDH staff reported 100 tweets from Twitter Blue subscribers with hate speech. Then, the CCDH monitored whether these tweets — which contained racist, homophobic and neo-Nazi conspiracies — had been removed from the platform four days later, but only one had been removed. Then, Spiro accuses the CCDH of taking money from Twitter parent X Corp.’s competitors and government entities in an attempt to drive advertisers off of the platform.

Per the letter, Spiro wrote to the CCDH that X Corp. has “reason to believe that your organization’s operations—and thus its campaign to drive advertisers off Twitter by smearing the company and its owner—are supported by funding from X Corp.’s commercial competitors, as well as government entities and their affiliates.”

The CCDH denied the claim, pointing out that it is illogical to suggest the organization is receiving money from other social media platforms when it has also published damning research about platforms like Facebook, Instagram and TikTok.

“Simply put, there is no bona fide legal grievance here,” wrote CCDH lawyer Roberta A. Kaplan. “Your effort to wield that threat anyway, on a law firm’s letterhead, is a transparent attempt to silence honest criticism. Obviously such conduct could hardly be more inconsistent with the commitment to free speech purportedly held by Twitter’s current leadership.”

TechCrunch contacted Spiro to confirm the letter uploaded by the CCDH did indeed come from his firm, but did not immediately get a response. Twitter’s parent company also recently threatened to sue Meta, claiming that it poached ex-Twitter employees to build Threads, its new microblogging app.