Friday's rally in Jakarta is expected to attract about 150,000 people who have been angered by allegations that Basuki Tjahaja Purnama insulted Islam, a criminal offence in the Muslim-majority country.
That would make it even bigger than a protest earlier this month that was marred by deadly violence.
Tens of thousands of people rallied in the capital on November 4 in the largest protest the city has seen for years.
It turned violent as night fell, with hardliners setting fire to police cars and battling with security forces, who responded with water cannons and tear gas. One person was killed and hundreds injured.
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"The aim of this event is to unite us. There have recently
been tensions among us, let's minimise that and come together again," said event organiser Zamroni, who like many Indonesians goes by one name.
Muhamad Amirudin, 30, said the event was a show of unity, adding, "We hope Friday's event will be equally peaceful."
The crowds consisted of military and police personnel, government officials and some members of the public, who listened to speeches and musical performances.
Police named Purnama a suspect in a blasphemy investigation earlier this month following the protest, as calls mounted from Muslim groups for him to be prosecuted for allegedly insulting the Koran while campaigning for governorship elections.
After studying the evidence handed to them by police, prosecutors said Wednesday Purnama, known by his nickname Ahok, would face court, as had been expected.
The governor, who is also a member of Indonesia's tiny ethnic Chinese minority, could be jailed for up to five years if found guilty.