Deputy Prime Minister Wissanu Krea-ngam says there are two approaches to amending the constitution -- with or without a referendum.
Mr Wissanu, a legal expert, said on Thursday that amendments requiring a referendum are changes to Chapter 1 which contains general provisions, Chapter 2 which deals with the monarchy and Chapter 15 which deals with constitutional amendments, including Section 256.
Changes to provisions associated with the qualifications and power of members of independent agencies, such as a provisional section allowing the Senate to join MPs in voting for a PM, also require a referendum.
Mr Wissanu said proposals to set up a charter drafting assembly are tantamount to amending Section 256 and require a referendum.
These amendments must be passed by parliament before being put to a referendum. It costs about 3 billion baht to hold one, he added.
Amendments that do not require a referendum are those unrelated to these chapters and provisions.
These changes will also go through a parliamentary mechanism under Section 256. If someone dispute the changes, they can ask the Constitutional Court for a ruling within one month.
If no one mounts a legal challenge, the amendments will be submitted for royal endorsement and come into effect.
There are still hurdles to organising a referendum. Currently there is no law on holding a referendum. Passing legislation will require time.
The referendum law under the previous 2007 constitution is no longer in use as the 2007 charter was abrogated.
The 2016 referendum law was enacted only for the referendum on the constitution in 2017 and is no longer in force.
The agency that is responsible for issuing a referendum law is the Election Commission (EC). Last year, the poll agency sent a bill on referendums to the government, which was in the process of presenting it to parliament.
But the National Legislative Assembly was dissolved after the general election.
Mr Wissanu added that the charter rewrite process is unlikely to take place during the current parliamentary session because parliament is still deliberating the budget bill for fiscal 2021.