Mass demonstrations are expected in Cairo later over the military's move to seize sweeping powers.
The Muslim Brotherhood has called for its supporters to head to Tahrir Square to join the protest, which is also backed by several revolutionary groups.
As polls closed in the country's close fought presidential election on Sunday, the ruling military issued a declaration granting itself the powers that were assigned to the parliament.
The military has ordered the dissolution of the Islamist-dominated legislature after a court ruled the parliamentary elections - completed six months ago - unconstitutional.
The move gives the military control over law-making, the budget, and the writing of a new constitution, which will effectively limit the new president's powers.
The Muslim Brotherhood's Dr Mohamed Morsi has claimed victory in the presidential election but the outcome is still being disputed ahead of official results on Thursday.
His opponent, Hosni Mubarak 's former prime minister, Ahmed Shafiq, has refused to concede defeat despite tallies suggesting he is trailing by almost one million votes.
A confirmed win for Dr Morsi would herald in Islamist rule in Egypt for the first time.
The Muslim Brotherhood believes the military council, which has been ruling the country since the revolution 16 months ago, is trying to frustrate the transition from military to civilian rule.
The Supreme Council of the Armed Forces (Scaf) has insisted that it will hand over power to the new president by June 30.
It has sought to play down claims of a power grab by saying that its control over legislation will simply act as a "balance"on the president that the parliament would have performed.
The Muslim Brotherhood has demanded the reinstatement of the legislature which is being guarded by riot police who have been ordered to keep the MPs out.
Revolutionary groups have termed the military's move a "coup" but many young secular activists are also uneasy at the prospect of the Muslim Brotherhood taking the presidency.
