The Lycée Brassens à Evry (Essonne) is now under police protection while an investigation takes place, and the letter was seized for forensic analysis, according to French media reports.
Addressed to the head teacher, the letter read: "Your teacher, Mr [redacted], the dirty Jew, should stop being clever. We are going to do a Samuel Paty [the French teacher who was beheaded] on him and his father, the old Zionist rabbi.
"We don't want Jews in our high schools; stay in your synagogues. We will deal with [redacted] at the exit of the school."
The letter was shared in full on Twitter by Yonathan Arfi, President of Le Crif, the French equivalent of the Board of Deputies.
Mr Arfi wrote: "What I don't want in high schools is antisemitism, the rejection of the Republic, hatred of teachers...
"Two years after the Islamist assassination of Samuel Paty, sending support to teachers who are still targets."
According to police and judicial sources who spoke to BFMTV, there was no discussion of any sensitive or controversial topics in the teacher's classes that could have triggered the threat.
CNEWS also reports that there have been no recent incidents involving the teacher and any students or parents.
The Lycée Brassens à Evry is located just south of Paris (Image: Google Maps)
While the investigation is ongoing, the school remains under police protection, as does the teacher whose home is also being protected by the police.
This incident comes as French schools prepare to pay tribute to history teacher Samuel Paty this week.
Paty was murdered and beheaded on the 16th of October 2020 by an Islamic terrorist after he was accused by a student of showing Charlie Hebdo's 2012 cartoons depicting the prophet Muhammad in class.
The perpetrator, Abdoullakh Abouyedovich Anzorov, an 18-year-old Russian Muslim refugee, was shot dead by police minutes after the attack. 10 people have since been charged with conspiring with and assisting the killer, including an imam, a parent of a student, and two students at Paty's school.
