The national lawyers' association said it supports Saturday's action by the judges' group, The New York Times reported.
Thousands of activists joined protests in Cairo Saturday and petitions were filed asking Egypt's highest court to overturn Morsi's decree.
Abdel Meguid Mahmoud, a prosecutor named by former President Hosni Mubarak, spoke to an enthusiastic crowd of judges. He accused Morsi of a "systematic campaign against the country's institutions in general and the judiciary in particular" and said the decree is "null and void."
Earlier Saturday, 13 petitions were filed asking a court to declare Morsi's action unconstitutional, al-Masry al-Youm reported. They argued the president cannot place himself above the law by decreeing himself immune from the courts.
Protesters from a range of parties clashed with police and with unidentified assailants supporting the president, Ahram Online said. Most of the confrontations took place around Tahrir Square, where thousands of protesters converged Friday to denounce Morsi's decree, with many saying it bordered on dictatorship.
Protesters gathered in front of the Judiciary General Assembly, chanting "the people demand the downfall of the regime," Ahram said.
Scores of demonstrators had trouble breathing due to the use of tear gas Saturday, the Egypt Independent reported. Officials at Mounira Public Hospital said 32 people were being treated for injuries and five people were in critical condition from gunshot wounds, although there were no police reports of shots being fired.
State television quoted the Interior Ministry as saying 210 protesters had been arrested by late morning, 44 of them juveniles.
Protesters shouted that Morsi, 61, a member of the Muslim Brotherhood, is no better than the autocratic former President Hosni Mubarak, who was unseated last year.
Morsi was elected in June.
His proclamation Thursday said neither parliament nor the courts can overturn anything he has done or will do until a new constitution can be approved in about six months.