The UEJF on Friday said that Twitter had agreed to take down many offending tweets that have recently flooded the site.
They bore the hashtag #unbonjuif (#AGoodJew), frequently followed by comments such as: "#AGoodJew is a dead Jew".
But UEJF lawyer Stephane Lilti told AFP Monday that 50 new messages were sighted over the weekend using a new keyword #unjuifmort (A Dead Jew).
"We are giving a few days for these tweets that we have drawn attention to to be taken off," Lilli said.
France's SPCJ Jewish security watchdog said two weeks ago that anti-Semitic acts surged by 45 percent since the start of the year and were given fresh impetus by attacks by Islamic extremist Mohamed Merah.
Merah went on a shooting rampage in March in and around the southern city of Toulouse, killing a rabbi, three Jewish children and three French paratroopers -- two of them Muslim -- before being shot dead in a police siege.