"It is trying to impose a constitution monopolized by one trend and is the furthest from national consensus, produced in a farcical way," the National Salvation Front said in a statement, read by Waheed Abdel-Meguid, one of the assembly members who withdrew.
Thursday's vote also escalates an already bruising confrontation sparked last week when Morsi gave himself near absolute powers that neutralized the judiciary, the last branch of the state not in his hands.
The result has been one of Egypt's worst bouts of turmoil since last year's fall of autocrat Hosni Mubarak, pitting Morsi and his Brotherhood supporters against a mostly secular and liberal opposition and the powerful judiciary on the other.
Street clashes have already erupted between the two camps the past week— and more violence is possible. At least 200,000 people protested in Cairo's Tahrir square earlier this week against Morsi's decrees.
The opposition plans another large protest for Friday, and the Brotherhood has called a similar massive rally for the following day, though they decided to move it from Tahrir to avoid frictions. Hundreds of opposition supporters have been camping out since Friday in Tahrir and bands of youths have been daily battling police on a road leading off the square and close to the U.S. Embassy.
Morsi's edicts aimed at preventing the judiciary from disbanding the constitution-writing panel. He barred courts outright from doing so, then went further to bar judges from reviewing any of his own decisions. Confident the assembly was protected, he gave it until February to iron out the sharp differences over the draft.
But when the Constitutional Court defied his decree and said Wednesday that it would rule on the panel's legitimacy, the date of the vote was immediately moved up.