"Moving a flawed and contradictory draft to a vote is not the right way to guarantee fundamental rights or to promote respect for the rule of law," said Joe Stork, deputy Middle East and North Africa director at Human Rights Watch.

Mohamed Naeem, a member of the Egyptian Social Democratic Party, said he fears the proposed constitution would open the way for a theocracy by moving the country closer to Sharia law.

The preamble includes language pertaining to women, saying they are equal to men, but it also accentuates their role as mothers.

And the United Nations' high commissioner for human rights, Navi Pillay, has urged Morsy to reconsider the draft, saying a number of measures contained in it are incompatible with international human rights law.

Beyond the details about the constitution itself, some see this month's vote more generally as a referendum on the government.

Morsy took office in June as Egypt's first popularly elected president, following decades in which Mubarak held vast powers and limited dissent (including by banning the Muslim Brotherhood). But Morsy's recent moves have stirred suspicions that he and his Islamist allies are intent on amassing powers at the expense of others.