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 2022.
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.
BBC News has contacted the company for comment.
"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."
The case will try to determine whether Twitter is contractually obliged to remove such material.
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."
In 2021, before Mr Musk bought Twitter, the Campaign Against Antisemitism, with which it had partnered, said the company's policies were failing - and it had removed only 400 of 1,000 tweets containing hateful content attacking Jews.
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".
Boris Johnson, then Prime Minister, said social networks needed to "go further and faster to remove content like this".
Other big social networks, including Facebook, Instagram and TikTok, have faced similar accusations.
Under the UK Online Safety Bill, technology companies would face large fines for failing to swiftly remove hateful content.
Culture Secretary Michelle Donelan hopes the bill will be passed into law this summer.