By Frances Harrison
BBC News, Tehran
Forty professors and lecturers from Tehran University in Iran are being retired on Thursday.
The ayatollah says the choices are not politically motivated
The move is causing concern that the new government of President Ahmadinejad is purging professors.
Last year, there were protests after he appointed an ayatollah as chancellor of the university - the first time a cleric had been put in charge.
The chancellor says there is nothing political or religious about the choices for retirement.
Ayatollah Abbas Ali Ameed-Zanjani said those who were retiring should be warned in advance that in Iranian culture retirement was like early death - hardly comforting words.
He said those leaving come from both the radical left and right and were chosen because they were over 65 years of age and could be replaced easily.
Asked how he managed to remain as chancellor at the age of 68, Ayatollah Ameed-Zanjani said it was not up to him.
'Whipped up emotions'
He said not all those leaving were full professors and he questioned critics who said that the 40 teachers were highly skilled, saying there needed to be a definition of those skills.
The chancellor also complained some professors had whipped up the emotions of students.
Those teachers, he said, would not be allowed to work any more, but those who had not protested might be able to do some casual work in future.
One of the grievances during a brief spell of student unrest recently in Tehran was the retirement of so many professors from the university.