Pro-democracy demonstrators on Saturday demanded that parliament pass a charter amendment bill sponsored by civil group Internet Law Reform Dialogue (iLaw), saying the proposal was tantamount to being a voice of the people.
The protesters zeroed in on the charter issue at Democracy Monument rally, while reiterating their original three-point demand for a charter rewrite, the prime minister's resignation and reform of monarchy.
Their call came ahead of parliament's two-day session on Tuesday and Wednesday, when MPs will scrutinise six amendment bills as well as iLaw's. A charter amendment bill needs the support of at least one-third of the 250 senators or 84 to get through the first reading.
The iLaw draft, which includes calls for the abolition of seven organic laws written under the current charter, was initially signed by 100,732 people when it was handed to the parliament president. More than 700 people later withdrew their support for it.
According to the protesters, iLaw's version must be passed without drastic changes and parliament should clear the way for the charter writers to "re-draw every provision and every chapter".
They said the power of the 250-member senate appointed by the now-defunct National Council for Peace and Order (NCPO) must be curtailed and a drafting assembly to draw up a new constitution must be elected, or the process would be only a political show.
"The charter amendment draft proposed by iLaw is like the voice spoken by ratsadon [the people], with the signatures of more than 100,000 people as evidence," read the protesters' statement.
"This charter amendment draft is important and we insist it must not be shot down or altered. Every mechanism and every bent rule designed to prolong power must be removed."
Parit Chiwarak, a key member of the People's Movement, took the stage about 8pm and reiterated that the PM must resign and clear the path for the charter amendment.
Thanathorn Juangroongruangkit, co-founder of the Progressive Movement, who attended the protest, said calls for charter amendments were growing louder and if they were not answered the people's anger would only grow.
The statement was read at the "Mob Fest" protest at the Democracy Monument.
The protest activities on stage kicked off after the royal motorcade of Their Majesties the King and Queen had passed, at which point the protesters turned their backs on the royal motorcade and sang the national anthem.
Some protesters later climbed on to the monument and covered it with a large cloth carrying messages.
According to Lopnapat Wangpaisith, leader of the Bad Students group which joined the Mob Fest rally after holding a protest outside the Education Ministry, those messages reflected "the people's will".
About 5,200 police officers were deployed to provide security from the Royal Plaza to Sanam Luang.
Pol Lt Gen Phukphong Phongpetra, chief of the Metropolitan Police Bureau, said there were no plans to disperse the protesters and officers had merely been deployed to maintain peace and order.
He also said the Royal Thai Police (RTP) would study the song "Patiroop" (Reform) produced by hip hop group Rap Against Dictatorship.
The song, which was uploaded to YouTube on Friday, had been viewed by more than 1million people by Saturday.