"No official has the right to order a young lady to remove a form of dress that was sanctioned by none other than Umar ibn al-Khattab, except for the purposes of identification for security reasons," he said.
"The niqab [face veil] is not in contravention of the sharia or Egyptian law."
Shaikh Safwat Hijazi, a scholar and preacher, said he would personally sue anyone who prevented his daughter or wife wearing full niqab from going about her daily life, including entering government offices.
"Preventing a woman from wearing what she wants is a crime," Hijazi said. "Whoever says the niqab is a custom is not respectable."
Husam Bahgat, of the Egyptian Initiative for Personal Rights, said the series of government decisions against the niqab are "arbitrary" and while designed to combat extremism, only end up being discriminatory against women.
"[Veiled female students] are barred from government subsidised housing and nutrition because they are considered extremists," he said.
But other Egyptian scholars, such as the ISI's Abd ul-Hamid al-Atrash, said there would be nothing wrong with such a ruling at a time when the anonymity afforded by the face veil was being abused by people intent on causing trouble.
"There have even been instances of men entering [schools for girls] under cover. So there is no reason why a ruling that benefits the people and the nation cannot be issued", al-Atrash said.
And Abd ul-Moati Bayumi, a scholar in an al-Azhar affiliated research centre, said most scholars would back Tantawi if he issued the order.
"We all agree that niqab is not a religious requirement," Bayoumi said. "Taliban forces women to wear the niqab ... . The phenomena is spreading" and it has to be confronted.
"The time has come."
Some scholars, such as Shaikh Abd ul-Dhahir Ghazala, were so surprised by the debate that they refused to believe that the chief Egyptian mufti, Muhammad Tantawi, would ever ban an article of clothing.
But security officials have reportedly told police that there are standing verbal orders to bar girls covered from head to toe from entering al-Azhar's institutions, including middle and high schools, as well as the dormitories of several universities in Cairo.
The measure is aimed at a minority of women, as a vast majority of Egyptian women wear the headscarf only.
Tantawi's plans came to light when he told a middle school student in a class he was visiting earlier this week to take off her niqab, according to details of the visit published by the independent daily AlMasry AlYoum.
However, a previous directive by the minister of religious endowment to ban women preachers wearing the niqab from mosques was hotly contested. A ban on nurses wearing full veil was announced last year, but not enforced.
A researcher wearing the niqab prevented from using the library at the American University in Cairo in 2001 took her case to the Egypt's supreme court and eventually won. The court ruled a total ban on the niqab to be unconstitutional.
The court did recommend that women wearing the niqab be made to uncover their faces before female security guards to verify their identity.
On Saturday, scores of female university students protested outside al-Azhar university dormitory calling for the repeal of the decision banning fully veiled women from entering. There were similar demonstrations at Cairo University.