More demonstrations are scheduled in Tahrir Square on Friday.
Fekri Mahkroub, a criminal court judge in Egypt's Ismailia district, said Thursday night that he was "sad because what President Morsy did is an assault on the legislative and judicial system."
"He defies anything the revolution stands for, and his actions are an insult to us as judges," Mahkroub said. "Declaring that his laws cannot be questioned is unacceptable, and we may see a general judicial strike."
Eric Trager, a fellow with the Washington Institute for Near East Policy, said Morsy not only is preventing the judiciary from overruling his decisions, but he also has "insulated the Muslim-Brotherhood-dominated (constitutional panel) from judicial oversight."
Depsite the protests in Cairo and objections from political rivals, Morsy -- elected with nearly 52% of the vote in a June runoff against former Prime Minister Ahmed Shafik -- enjoys the "best mobilizing capability in the country" in the Muslim Brotherhood, Trager said.
"If there's a nationwide movement against this, you'll (also) have a nationwide movement for it," Trager said.
After he was elected, Morsy took legislative control from the Supreme Council of the Armed Forces, which had ruled after Mubarak was deposed. Earlier, the council dissolved parliament's lower house, saying parliamentary elections that began in November 2011 were unconstitutional. Morsy indicated in June he would call back parliament, but Egypt's high administrative court upheld the dissolution.
Mubarak and his former Interior Minister Habib El Adly were convicted and sentenced in June to life in prison on charges relating to the deaths of hundreds of protesters after a 10-month trial, while six former government aides were acquitted. Some Egyptians protested the sentences and acquittals.
Morsy, who still was running for office, said at the time that he would initiate new investigations if elected.
About 840 people died and more than 6,000 others were injured in last year's 18-day uprising, according to Amnesty International.