Liberal, leftist and socialist forces have called for a "Last Warning" march to Egypt's presidential palace on Tuesday against a draft constitution written by an Islamist-led assembly.
An Islamist-dominated constituent assembly finished drafting the country's new charter on Friday morning allowing it to be put to referendum on December 15.
In a statement, several opposition groups also denounced a constitutional decree issued by President Mohamed Mursi, insisting that their protest will continue until their demands are met.
They warned Mursi that his legitimacy as president is wearing thin as a result of his performance and biased policies to the Muslim Brotherhood to which he belonged.
The statement accused the constituent assembly of lacking legal, political and popular legitimacy, describing the charter it drafted as a "project to restrict the political, civil, economic and social rights and freedoms" while only representing one segment of society.
"The Egyptian people and its political and revolutionary forces cannot accept a referendum to abort the revolution and its values and goals. Or a referendum that aims to erode democracy and limit it only to ballot boxes (that is if the vote is actually transparent and free). Or a referendum that threatens the freedoms and rights of Egyptians.
"It is unacceptable for the people to vote on their freedom, dignity and rights, especially in light of the current condition where Mursi broke his promise which was to only put the constitution to referendum following national consensus." The statement said.
The opposition urged all forces from different governorates to participate in Tuesday's demonstrations to protest Mursi's constitutional decree and the draft constitution.
They held the authorities responsible for securing the scheduled march.
The statement was signed by the Dostour Party, the Popular Current Party, the People's Socialist Coalition Party, the Social Democratic Party, Kefaya, the April 6 Movement, the Democratic Front among other parties and movements.