More than 1,000 people are expected to meet on Sunday at Thammasat University's Tha Prachan campus to discuss strategy for opposing the government's blanket amnesty bill.
Activist Suriyasai Katasila, a coordinator of the Green Politics group, said People's Network representatives from all 77 provinces were expected to attend the event.
Mr Suriyasai said the morning session would be devoted to assessing the current situation. In the afternoon, he expects participants will set a date and formulate a plan for nationwide rallies against the bill.
He and other critics say the revised amnesty bill, proposed by the Pheu Thai Party, was aimed at whitewashing ousted former premier Thaksin Shinawatra.
The bill passed first reading in the House earlier and was amended further by a committee dominated by Pheu Thai members. The most contentious amendment would nullify the decisions of groups set up by those who staged the 2006 coup that ousted Thaksin. That would cover the Assets Scrutiny Committee, whose findings led to the court order to seize 46 billion baht in assets from Thaksin.
The second and third readings of the bill are expected to take place in the House in November.
Mr Suriyasai claimed that the Interior Ministry was trying to stop activists from meeting by falsely claiming that the amnesty bill would create national reconciliation.
But the bill would benefit only Thaksin and it would lead to more social divisions, he said. These concerns would encourage more people's groups to join the rally, he added.
The revised bill proposes to grant a blanket amnesty to all involved in the 2010 political violence, including protest leaders, soldiers, authorities and Thaksin.
Tida Tawornseth, chairwoman of the red-shirt United Front for Democracy against Dictatorship (UDD), said on Friday that the UDD opposed amnesty for former premier Abhisit Vejjajiva and his deputy Suthep Thaugsuban.
She insisted that those who ordered the use of force to crack down on red-shirt protesters in May 2010 must be punished.
Relatives of those killed during clashes between red-shirt supporters and security forces in May 2010 took the same tone, saying that those behind the violent crackdown must face the legal consequences.
The opposition Democrat Party also strongly opposes the bill, saying that only Thaksin would benefit.
However, Justice Minister Chaikasem Nitisiri supports the bill and says it is the best way to extract the country from ongoing political conflict.