French anti-racist organisations are considering suing Twitter users after the hashtag #unbonjuif, which means a good Jew, went viral on the microblogging site to become the third most popular among French Twitter users.
Offensive comments have flooded Twitter with a sort of "competition of anti-Semitic jokes", French daily Le Monde wrote.
MRAP and SOS Racisme, two major anti-racist organisations in France, said they were outraged. On their websites they pledged to sue Twitter users sending anti-Semitic tweets.
MRAP demanded that Twitter should "take the appropriate measures" to end what it called a flood of anti-Semitism.
Offensive tweets under the hashtag included "A good Jew can pump up your tyre with his nose" and "A good Jew is a dead Jew".
A user called Marcel Leblanc posted a picture of an emaciated Jewish woman who had been incarcerated in a Nazi concentration camp along with the caption, "A good Jew".
Jonathan Hayoun, president of the Union of French Jewish Students, called on Twitter to "put in place a new system to moderate" anti-Semitic tweets.
Jewish campaigners have warned of an thickening atmosphere of anti-Semitism in parts of France with attacks on synagogues and Jewish supermarkets in recent months.
On 10 October, police swooped on a bomb-making factory in Paris believed to be used by a radical Islamist group who were tracked after a grenade attack on a Jewish supermarket in September.