Elon Musk has threatened to sue the Anti-Defamation League after accusing the US-based civil rights group that campaigns against antisemitism and bigotry of trying to “kill” his X social media platform. The owner of X, formerly known as Twitter, said the ADL was trying to shut down his company by “falsely accusing it and me of being antisemitic”. In a series of posts on X, Musk said advertising sales for the business were down 60% and “based on what we’ve heard from advertisers, ADL seems to be responsible for most of our revenue loss”. The world’s richest man also indicated that he would sue the group for defamation, posting on X that “it looks like we have no choice but to file a defamation lawsuit against the Anti-Defamation League … oh the irony!” Musk recently sued another anti-hate speech group, the Center for Countering Digital Hate, in a lawsuit accusing it of damaging X’s relationship with advertisers. CCDH has said it will fight the lawsuit and keep holding “Twitter’s feet to the fire”. In his posts on Tuesday, Musk added that to be “super clear” he was in favour of free speech “but against antisemitism of any kind”. The ADL describes itself as the world’s leading anti-hate organisation and says its mission is “to stop the defamation of the Jewish people and to secure justice and fair treatment to all”. According to the group, antisemitic posts on X increased sharply after Musk bought the site in October 2022 and the platform subsequently reinstated extremists and conspiracy theorists, while allowing the harassment of former members of its now-dissolved trust and safety council. One legal expert said Musk could attempt to sue for defamation under US state law but is unlikely to succeed. “Whether or not someone is antisemitic is fundamentally a matter of opinion, which is protected expression. Elon’s threats of litigation seem to be in effort to dissuade ADL from perpetuating a message he does not like,” said Jennifer Safstrom, a professor at Vanderbilt University law school. Linda Yaccarino, the chief executive of X, said last month that the platform had become a safer place under Musk’s ownership. “By all objective metrics, X is a much healthier and safer platform than it was a year ago,” she said. Yaccarino, a highly respected TV advertising executive, was appointed in May with the task of restoring relationships with advertisers a priority. In 2021, advertising accounted for 90% of X’s revenue but that income stream has been hit by companies pausing ad spending over doubts about Musk’s leadership. The carmaker Audi and the pharmaceuticals group Pfizer were among the brands that have boycotted X amid concerns about the platform’s stance on content. X has reinstated previously banned users such as the misogynist influencer Andrew Tate and also botched a relaunch of its subscription product, which resulted in a spate of impostor accounts. An ADL spokesperson said the organisation does not comment on legal threats as a matter of policy.