A French court has stated that Twitter must help identify the authors of anti-Semitic tweets posted under the hashtag #unbonjuif, which means 'a good Jew' in French.
The ruling follows a legal complaint issued by France's main Jewish student union, the UEJF, who also urged more robust use of French laws on illicit content.
Twitter has already agreed to delete the racist messages that flooded the site in a "competition of anti-Semitic jokes", French daily Le Monde wrote. The hashtag became the third most popular among French Twitter users.
With Thursday's ruling, Twitter will be forced to hand over data to help identify the authors of the messages.
Twitter refused at the time to comment directly on the tweets, and said that the company "does not mediate content".
"If we are alerted to content that may be in violation of our terms of service, we will investigate each report and respond according to the policies and procedures outlined in our support pages," a spokesperson said.
Twitter also said it would not hand over details of account holders unless ordered by a judge.
However, in October Twitter applied its local censorship policy for the first time by blocking access to a neo-Nazi account to users in Germany.
With the messages posted on the far-right Besseres Hannover account, Twitter enacted its new policy on censorship, whereby accounts can be blocked in individual countries if the content violates local law. The policy was announced in January, and has never previously been enacted.