The start of overseas voting after nearly three weeks of mass opposition protests showed the determination of Morsi to go forward with the process despite outrage from the liberal opposition, which contends it places restrictions on liberties and gives Islamists a big say on how the country is run.
The opposition front had been expected to call for civil disobedience, such as general strikes, to escalate the recent mass protests against Morsi. Mass rallies are scheduled for Friday, on the eve of the vote.
The opposition has been considering several options to force Morsi to back down and postpone the vote.
Ahmed Khairi, a spokesman for the liberal Free Egyptians party — a member of the National Salvation Front — said the party had been in favor of a boycott.
"There were several points of views, but as long as everybody agreed on going for 'No,' we changed our position," he said. Other options, such as more rallies and civil disobedience, remain on the table.
"The constitution is a decisive battle but not the final one. We will keep on fighting for our demands and for Egypt to become a country for all. This will not be the end," he said.
Islamists who support the draft constitution, led by Morsi's Muslim Brotherhood and the ultraconservative Salafis, have been distributing flyers urging a "Yes" vote along and putting up posters with the same message. They have been also been using mosques to disseminate their message.
Several hundred Islamists loyal to Morsi have meanwhile been staging a sit-in outside a media complex known as "media city" on the outskirts of Cairo. The complex is home to some of the most influential independent TV networks critical of the president and his Muslim Brotherhood. The Islamists are threatening to storm the complex.
In a move likely to stoke the judges' anger, Egypt's top prosecutor, Morsi appointee Talaat Abdullah, removed the judge in charge of an investigation into the violence outside Morsi's presidential palace last week which began when Islamists loyal to the president set upon opposition protesters staging a sit-in. The judge, Mustafa Khater, had ordered the release from detention of most suspects for lack of evidence, a move that drew public criticism from Mohammed Badie, the influential head of Morsi's Muslim Brotherhood.
Human Rights Watch, meanwhile, called on authorities Wednesday to investigate the detention and abuse of opposition protesters by Brotherhood supporters last week outside the presidential palace. It accused Morsi of violating the due process rights of suspects detained in connection with the violence by referring to their "confessions" to be "hired thugs" in a televised speech.
The opposition has been boycotting a "national dialogue" hosted by the president, saying they don't trust Morsi after he failed to live up to promises during the election campaign to form a representative national coalition government and to win a broad consensus before putting the constitution to a vote.
In another twist, Egypt's military withdrew a call for talks with the opposition, one day after proposing it.
Military spokesman Col. Ahmed Mohammed Ali was quoted by the official MENA news agency as saying Defense Minister Abdel-Fatah el-Sissi decided to postpone Wednesday's meeting because "the response to the invitation was below expectations." The statement was not explained further.
"Lt-Gen. el-Sissi would like to seize this chance and call on all national and political forces and every segment of the glorious Egyptian people to shoulder their responsibility toward the nation and the citizens at this critical and sensitive time," Ali said.
That announcement came at the same time the opposition said it was willing to attend the meeting.
El-Sissi's call, in the midst of dueling mass protest for and against the constitution, was seen as a return of the powerful military to the political scene after Morsi's election ended nearly 17 months of military rule following Hosni Mubarak's February 2011 ouster. It was the second time this week the generals have addressed the crisis, signaling their return to the political fray.