There is no law allowing for the results of a referendum to decide whether the country should have a new charter, a former charter writer said.
The existing law, the 2009 Referendum Act, only allows for consultative referendums to be conducted, said Komsan Phokong, a law expert of the Sukhothai Thammathirat Open University. Consultative referendums are not legally binding.
However, to decide whether there should be a new constitution requires an absolute referendum, and no law exists to accommodate that.
Mr Komsan said a new constitution would involve a significant restructuring of the country's administrative powers and this requires a specific referendum.
The country had an absolute referendum law back in 2006. It was written in the interim charter, in effect following the coup that toppled Thaksin Shinawatra.
However, the absolute referendum law has not been incorporated in the current charter promulgated since 2007.
Mr Komsan also noted an amendment to Section 291 of the charter, which is awaiting clearance in the third and final reading in parliament, does not contain any clause on the absolute referendum.
An amendment to Section 291 would clear the way for the establishment of a drafting assembly to rewrite the charter.
The former charter writer said to rectify the problem, parliament has to first vote down the Section 291 amendment bill and then propose a new bill that includes a clause on the absolute referendum.
The clause must also authorise either the Election Commission (EC) or the Supreme Court's Election Division to organise an absolute referendum and to have the final say on the result of the referendum.
Meanwhile, election commissioner Sodsri Satayathum said the 2009 Referendum Act provides leeway for an absolute referendum to be held.
She said Section 165 of the law leaves open a loophole making the result of the referendum legally binding rather than merely serving a consultative purpose.
Ms Sodsri said the referendum question must have total clarity. She said it must inquire whether the entire charter should or should not be amended, and referendum questions put to voters must be unequivocally worded to avoid confusion.
She also estimates the referendum will cost between 1.7 billion baht to 1.8 billion baht to organise. The figure is based on the budget of the previous referendum in 2006.
In the previous referendum, the government allotted 1.2 billion baht to the EC and another 500 million baht for educating the public about the new charter.