The High Constitutional Court (HCC) is expected to decide on Tuesday on the constitutionality of Egypt's upper house of parliament, the Shura Council.
Amid a heavy police presence, dozens of protesters gathered outside the HCC on Tuesday morning to safeguard the court from potential disruption.
The April 6 Youth Movement, the Free Egyptians Party and the Egyptian Popular Current are among the groups that announced their participation in the protest.
The lower house of parliament was dissolved last summer after the HCC ruled against its constitutionality.
On 22 November, President Mohamed Morsi issued a constitutional declaration making Egypt's Constituent Assembly (tasked with drafting a new constitution) and Shura Council immune from dissolution and protecting his decisions against judicial appeal.
In late November, hundreds of thousands took to the streets to protest the proposed constitution and Morsi's constitutional declaration.
Morsi supporters laid seige to the HCC to prevent judges from issuing a ruling on the Shura Council, leading the court to freeze all its sessions indefinitely.
At the beginning of Tuesday's session, the head of the court, Judge Maher El-Beheiry, said, "We will not forget the unlawful seige, and the court will remain the guardian of the constitution and the law."
The Shura Council, which holds legislative power until the election of a new House of Representatives (lower house of parliament) in April, now awaits Tuesday's ruling.
Hossam Fouad, secretary of the Free Egyptians Party's youth committee, said in a statement released by the party on Saturday that party members would "participate in a peaceful protest to affirm the independence of the judiciary and support the constitutional court in performing its role."
Fouad added that the party supported any activity aimed at protecting justice, the rule of law and the sovereignty of the judiciary, regardless of the nature of its verdicts.
Members of political parties, revolutionary and national movements and individual activists set out from Cairo's Maadi district to the nearby HCC building at 5pm on Monday.
According to Al-Ahram's Arabic website, Interior Minister Mohamed Ibrahim visited the HCC Monday morning to conduct security measures. Ibrahim also met with police in the area, asking them to step up efforts to protect vital state institutions.
The Egyptian Popular Current, the political coalition created by former presidential candidate Hamdeen Sabbahi, had announced plans to participate in the sit-in last Thursday to protect the court and its judges from alleged Muslim Brotherhood militias.