Twitter is being sued in Germany by two groups claiming the social network failed to remove six posts attacking Jewish people and denying the Holocaust, after they were reported.
The posts were published after billionaire Elon Musk bought the platform in October 2021. But his tweets, which now represent most of the company's communications output, have not mentioned the case.
Antisemitism and Holocaust denial are illegal in Germany. They also violate Twitter's own terms and conditions.
"Twitter has betrayed our trust," said Avital Grinberg, the president of the European Union of Jewish Students (EUJS), which has brought the civil action, alongside HateAid.
"By allowing hateful content to spread, the company fails to protect users - and Jews in particular."
HateAid legal head Josephine Ballon said: "Twitter assures it won't tolerate violence on its platform. Users have to be able to rely on that."
The previous year, Twitter was criticised as too slow to remove tweets by UK musician Wiley that he later apologised for, saying they "were looked at as antisemitic".