More than 100 mainly Islamist lawmakers have walked out of Egypt's parliament in protest at constitutional changes they say will stifle opposition.
The lawmakers say the changes will undermine basic rights
The government says that the changes will deepen democracy and the rule of law in the country.
But almost a quarter of the 454-member parliament say they are a way for the president to maintain control.
The changes include a ban on the creation of political parties based on religion and sweeping security powers.
"We have decided to boycott these sessions to clear our conscience... and let the National [Democratic] Party bear the responsibility before the people," said Mohammed Saad al-Katatni, head of the Muslim Brotherhood's parliamentary group.
Egypt's parliament approved the changes in principle on Sunday.
They are expected to be passed by the legislature, dominated by President Hosni Mubarak's governing party, later next week.
The proposals will then be put to a referendum.
The amendments, which include changes to 34 articles of the constitution, will also allow the drafting of a new anti-terrorism law to replace the emergency legislation in place since 1981.
They will ban the establishment of religious parties, allow the adoption of a new election law and do away with the need for judicial supervision of every ballot box.
President Mubarak and other government officials say the changes will give a boost to democratic practice in the country.
But the opposition, which includes the illegal but popular Muslim Brotherhood, says the changes will consolidate dictatorship.
They say that watering down judicial supervision of elections will make fraud easier.
They are also deeply uneasy about the wording of the articles on the new anti-terrorism law because it will be possible to bypass the constitutional guarantees protecting basic freedoms.
Human rights group Amnesty International has called the changes the greatest erosion of human rights in 26 years.