Egypt's highest court has asserted its ruling that led to the disbanding of parliament is final and binding, state television said, setting up a showdown with the new president.
President Mohammed Morsi has recalled the parliament dissolved by the tribunal last month.
Monday's brief TV report followed a meeting by the Supreme Constitutional Court to discuss Mr Morsi's surprise decision.
It came just hours after the speaker of the dissolved legislature, Saad el-Katatni, called for the chamber to convene on Tuesday.
The announcement on state TV came a day after Mr Morsi recalled the legislators, defying the powerful military's decision to dismiss parliament after the Supreme Constitutional Court ruled that a third of its members had been elected illegally.
However, both sides appeared together today at a military graduation ceremony. Mr Morsi sat between the head of the armed forces Field Marshal Hussein Tantawi and Chief-of-Staff Sami Anan. The three sat grim-faced for most of the ceremony, but Mr Tantawi and Mr Morsi exchanged a few words while seated on the reviewing stand.
The court's judges made the decision in an emergency meeting even as the speaker of the dissolved legislature, Saad el-Katatni, called for parliament's lower chamber, the People's Assembly, to convene on Tuesday. The court's ruling did not cover parliament's upper chamber, known as the Shura Council, which is largely toothless.
Both Mr Morsi and Mr el-Katatni are long-time members of the Muslim Brotherhood, a fundamentalist group that has long been at odds with the military and with other Islamists holds the majority of parliamentary seats.
The move to restore parliament appeared to be an effort to exert Mr Morsi's authority as president despite a series of moves by the military before his election aimed at limiting his powers.
The Supreme Council of the Armed Forces took over governing the country after Hosni Mubarak was ousted by a popular uprising last year and the ruling generals have come under criticism for being slow to hand over power to a civilian administration.
Mr Morsi's executive order made no mention of the court's ruling, restricting itself to revoking the military's decree to dissolve the chamber. That appeared to be an attempt to avoid being seen as flouting a legal decision. Presidential spokesman Yasser Ali said Mr Morsi's decision did not violate the court's ruling, according to the Middle East News Agency.
In a separate report, the agency said the court was due to look into several cases questioning the legality of Mr Morsi's decision to reconvene parliament.
The parliament building remained under police guard, although scores of Morsi supporters gathered outside on the street. Many Islamist politicians have said they would attend Tuesday's session. Secular politicians, however, were leaning towards a boycott.
"How can we go and attend in violation of a court ruling?" said Imad Gad, a liberal politician. "There must be respect for the law and for state institutions."
The Brotherhood, long repressed under secular regimes, has emerged as Egypt's most powerful post-Mubarak political force, winning nearly half the seats in parliament and putting their candidate in the president's office.
Mr Morsi's order left Egypt's political and judicial actors scrambling. Mr Morsi also called for new parliamentary elections within 60 days of the adoption of a new constitution, which is not expected before late this year.
The generals who make up the Supreme Council of the Armed Forces held an "emergency meeting" soon after the president's decision was announced on Sunday, but issued no statement.
The military announced a "constitutional declaration" last month giving itself legislative powers in the absence of parliament and stripping Mr Morsi of much of his presidential authority. In a rush of decrees shortly before formally handing over power to Mr Morsi on June 30, the generals also took control over the process of drafting a new constitution and the national budget.
Mr Morsi came to power after narrowly defeating Mubarak's last prime minister, Ahmed Shafiq, in a run-off last month.
Declared the winner on June 24, he symbolically took the oath of office five days later at Tahrir Square, birthplace of the revolt that toppled Mubarak's regime on February 11, 2011.
He took the formal oath the next day before the Supreme Constitutional Court and again at Cairo University before hundreds of his supporters, including many of the dissolved legislature's politicians.
In his inauguration speeches Mr Morsi hinted at his displeasure over parliament's dissolution and his own diminished powers, pointedly seating Mr el-Katatni, the speaker of parliament, in the front row during the Cairo University ceremony.