The 'Popular Current' has called on people to rally by the High Constitutional Court on Tuesday to defend the scheduled hearings where legal challenges against two Islamist-led bodies will be reviewed.
Egypt's highest court will review lawsuits filed against the assembly that wrote the new constitution and the Shura Council (upper house of parliament) on Tuesday.
In a Facebook statement, the Popular Current, founded by ex-presidential candidate and opposition figure Hamdeen Sabahi, called on people to rally to protect the court from "militias of the Muslim Brotherhood" so that the court can operate.
Islamists, including supporters of President Mohamed Mursi, put the court under siege at the beginning of last month, preventing it from issuing a ruling in the legality of the constituent assembly and the Shura Council.
This led the constitution-writing assembly to carry on and put the draft charter on a referendum and have it approved, when its legality is in fact in question.
A court order that struck down the parliamentary elections law led to the dissolution of the People's Assembly in June. The Shura Council however remains standing despite being elected according to the same invalid law that led to the dissolution of the assembly.
The Shura Council has assumed legislative power until the election of a new House of Representatives.