Thousands of people demonstrated noisily Saturday in Turkey's largest city against an attempt to have the ruling party legally outlawed.
The constitutional court is to begin hearing submissions next month in the case brought by the country's chief prosecutor against the Justice and Development Party (AKP) which he accuses of trying to install an Islamist regime.
The party's supporters say the country's secular forces are trying to stage a coup through the judiciary.
Saturday's demonstration was called by left-wing organizations, rights groups and Islamists and included a cross-section of people ranging from women in Islamic headscarves to students and intellectuals.
Prosecutor Abdurrahman Yalcinkaya is to appear on July 1 before the 11-judge constitutional court to argue why the AKP should be outlawed. On July 3, the AKP's representatives will deliver the party's verbal defense.
After the hearings stage, a court-appointed rapporteur will prepare a non-binding report on what verdict the judges should give. The court will then set a date to debate the case behind closed doors and reach a verdict.
The prosecutor launched proceedings in March against the Islamist-rooted AKP, arguing that it had become a "focal point" of anti-secular activity seeking to set up an Islamist regime in Turkey.
He also asked the court to bar 71 AKP officials, including Prime Minister Recep Tayyip Erdogan and President Abdullah Gul, from party politics for five years.
The AKP rejects the charges and says it is fully committed to the separation of state and religion enshrined in the constitution.
It says it has disowned its Islamist roots and embraced Turkey's bid to join the European Union. Many secularists however --including the army, much of the judiciary and some academic circles -- suspect the AKP of having a secret Islamist agenda.