Egypt's upcoming constitutional referendum will be held in two stages on 15 and 22 December, ordered a decree issued by President Mohamed Morsi on Wednesday.
The vote had earlier been scheduled for 15 December only.
In the first stage on 15 December, polling will take place in the governorates of Cairo, Alexandria, Daqhaliya, Gharbiya, Sharqiya, Assuit, Sohag, Aswan and North and South Sinai, according to the source.
On 22 December, polling will take place in the governorates of Qena, Beni Suef, Minya, Menoufiya, Beheira, Damietta, New Valley, the Red Sea, Fayoum, Kafr Al-Sheikh, Giza, Port Said, Suez, Marsa Matrouh, Luxor, Qalioubiya and Ismaliya.
A justice ministry source told Al-Ahram's Arabic-language news website that the decision to hold the vote in two stages had been based on a request by Egypt's Supreme Electoral Commission (SEC), which cited the limited number of judges available to oversee the poll.
A number of Egyptian judges have gone on strike following President Mohamed Morsi's 22 November constitutional declaration, which temporarily bolstered his powers.
On Tuesday, the Egyptian Administrative State Council's Judges Club declared its members' refusal to supervise Saturday's vote.
A presidential spokesman said the decision to hold the poll in two phases was made by the SEC, stressing that the presidency had no say in the move.