The two established political blocs, the National Democratic Party and Muslim Brotherhood, back the proposals.
But pro-democracy activists say the changes do not go far enough and want the plan rejected.
They say the constitution needs to be entirely rewritten before elections can be held.
Nobel Peace Prize winner Mohamed ElBaradei, who emerged as an opposition figurehead during the uprising, said the referendum dealt only with "minutiae".
"It doesn't talk about the imperial power of the president, it doesn't talk about the distortion of the parliament, it doesn't talk about the need to have an independent constituent assembly that represents everybody," he said in comments carried by AFP news agency.
"So we are going to say no. Most of the people who triggered the revolution are going to say no."
The NDP and the Muslim Brotherhood are on the same side of the constitutional referendum. Why am I not surprising?