Muhammad Ismail Yusanto, from Hizb ut-Tahrir, told Al Jazeera that a move away from secularism was needed.
"Indonesia has been living under secular ruling since it gained its independence and we have never had anything but misery and poverty. That is why we have been fighting to replace the secular system with an Islamic one."
Azyumardi Azra, from the State Islamic University, said that a move towards sharia was detrimental to the world's most populous Muslim nation.
"Introducing sharia bylaw is threatening to development, so that's why I appeal from time to time to the Supreme Court to investigate the so-called Sharia bylaw," Azra said speaking to Al Jazeera.
He said that implementing the regional implementation of bylaws was illegal and that the supreme court should reveal all these regulations.
Erni Tri, 40, a high school teacher attending the meeting said she drove for two hours with her husband and three children to join in the prayers, music and speeches.
Hizb ut-Tahrir "is firm and uncompromising toward un-Islamic cultures," she said.
"It is driven by love for Allah and has no hidden agenda to get votes or power."
The group, though radical, claims it does not support violence but is banned in some Southeast Asian and Arab countries.
Anick Hamimtohari, from the Liberal Islamic Network, said the movement was set up in the mid-90s and developed quickly through universities.
"Their militancy is extraordinary," he told Al Jazeera.
Imran Waheed and Sheikh Ismail al-Wahwah, speakers from England and Australia, were deported upon arrival in Indonesia, a spokesman said.
It was not immediately clear why they were not allowed to attend.