Andrej Holm, from Berlin's Humboldt University, who specialises in urban gentrification, was arrested three weeks ago on suspicion of aiding a militant organisation suspected of carrying out more than 25 arson attacks in Berlin since 2001.
In protest letters the academics from across Europe, the US and Canada said Mr Holm's arrest was based on his academic writings, and the evidence used to connect him to terrorism was at best flimsy.
The federal prosecutor's office arrested Mr Holm on August 1 under paragraph 129a of the anti-terrorism law, citing the repeated use of words such as "gentrification" and "inequality" in his academic papers, terms similar to those used by the urban activist organisation "militante gruppe" (mg). According to the prosecution report the frequency of the overlap between words used by Mr Holm and the group was "striking, and not to be explained through a coincidence".
It also cited the fact that he had twice met three men who were arrested on suspicion of involvement in an arson attack in Brandenburg on July 31 and who are accused of belonging to the mg. The prosecutor's office said it added to the "conspiratorial circumstances" that he did not take his mobile phone to the meetings.
The fact that he and another academic had access to a library meant they were "intellectually in a position to compile the sophisticated texts of the 'militante gruppe'," the prosecutor's office said.
In one of the letters, signed by more than 100 academics, the federal prosecutor, Monika Harms, was urged to release Mr Holm from his single-cell in Berlin's Moabit prison. "We strongly object to the notion of intellectual complicity adopted by the federal prosecutor's office in its investigation ... such arguments allow any piece of academic writing to be potentially incriminating," the academics said.
Mr Holm, 36, made a name for himself with his research into the effect of urban renewal on residential areas of the German capital since the fall of the Berlin Wall.
"The police may have solid knowledge they are withholding, but their public statements belong in the realm of farce," Richard Sennett, a sociologist at the London School of Economics, and Saskia Sassen, a sociologist at Columbia University, wrote on Guardian Unlimited's Comment is Free site. "This action in a liberal democracy seems more to fall into Guantánamo mode than genuine counterespionage."