"Mr Kordan was expected to present the necessary documents to prove the validity of his doctorate, but unfortunately it has not been done," Ali Akbar Javanfekr said, referring to the honorary diploma in law that the new minister says he was given by Britain's prestigious Oxford University.
Javanfekr called on Kordan "to take the fair and brave decision as society expects before others take the correct decision on this issue." He did not elaborate.
Ahmadinejad had initially leapt to the defence of the new minister, who was appointed only last month, saying that he should not be judged on the basis of a "piece of torn paper".
But he later ordered a probe into all academic qualifications obtained by government officials since 1985.
The case has proven controversial in Iran. A conservative website close to a prominent member of parliament was temporarily banned after it published Oxford University's denial last month that it had ever awarded Kordan any qualification.
Kordan was appointed last month after Ahmadinejad sacked his last interior minister in May in one of his numerous cabinet reshuffles.
