Supporters of Hassan Diab, a Canadian professor suspected in a deadly 1980 attack on a Paris synagogue, asked Prime Minister Justin Trudeau Thursday to encourage French authorities to release him.
"We urge you to intervene and bring Hassan home," said a letter to Trudeau signed by more than 600 people and organizations.
A petition delivered to the Canadian parliament calling for his release was also signed by thousands more.
Diab, 63, has been in pre-trial detention in France since being extradited from Canada in November 2014 and charged with the attack.
The bombing outside the Copernic Street synagogue was the first major attack on a Jewish site in France since World War II.
The Popular Front for the Liberation of Palestine (PFLP) was blamed for the blast that left four dead and some 40 injured.
Diab, a Lebanese-Canadian sociology professor, maintains his innocence and denies he was a member of the PFLP.
The investigation wrapped up in July, but the judge's decision on whether to drop the charges or proceed to trial is still pending, as the prosecution has yet to file written submissions in the case.
French investigative judges had on several occasions granted Diab bail, citing evidence that he was not in France at the time of the bombing, but each time those decisions were overturned on appeal.
"We are deeply concerned that Hassan may be wrongfully convicted under France's antiterrorism laws, based on deeply flawed handwriting analysis and the use of secret, unsourced intelligence," said the letter to Trudeau.
"Hassan must receive a fair process, so he has a real chance to attain justice and return to his home in Canada."