Morsy, who is backed by the Muslim Brotherhood's political party, has refused to delay the referendum, saying a constitution is essential for the fledgling democracy. The opposition, meanwhile, says the document does not represent all Egyptians.
The opposition has accused Islamists, predominantly the Muslim Brotherhood, of manipulating the poorer portions of the population, using a fear of God and religion to drive them to vote.
In an interview with CNN, al-Tahtawi, who also is backed by the Muslim Brotherhood, disagreed with the opposition's characterization, describing it as "part of the disease of the elite."
An independent judiciary has backed Morsy, finding that the referendum must be carried out on December 15 to meet a legal requirement.
Morsy canceled the edict that gave him virtually unchecked powers over the weekend, though he did not roll back the directives he put in place before it. Among the steps he took was setting the date of the constitutional referendum.
A coalition of Egyptian Islamic parties, including the Brotherhood, says it rejects any postponement of the vote. A countering coalition of Morsy's opponents, the National Salvation Front, called for protests Tuesday and Friday.