Pro-democracy campaigners are holding a rally in the Tongan capital of Nuku'alofa to highlight failings in the current constitution to coincide with Constitution Day.
Friday marks the 130th anniversary of the creation of the Tongan Constitution by King George Tupou I.
Pro-democracy MP, Akilisi Pohiva, says hundreds of people are expected to meet at the town centre, Pangai Si'i to hear from speeches from MPs, campaigners and church leaders.
Mr Pohiva says although there will be a festive mood the speakers will concentrate on the need for change.
"There are things very vital that are missing from the existing constitution and that would be a part of celebrations. We will have speakers and they will present their views regarding the need for a reform or the need for a change to our constitution to allow the people of Tonga to be part of the decision making or to have a share in running our government."
Pro-democracy MP, Akilisi Pohiva.