The telecom regulator plans to consider forcing all mobile operators to install a system or application to allow users to block incoming phone calls from abroad to combat call centre scams.
The proposal was made by a multilateral working group tasked with finding ways to tackle fraudulent call centres following its meeting on Tuesday.
Once approved, mobile operators will have 60 days to comply or face a penalty.
Prawit Leesathapornwongsa, head of the working group, said the proposal will be submitted to the board of the National Broadcasting and Telecommunications Commission (NBTC) next week as an urgent agenda item to address the problem.
Installing such a system would be made a condition for issuance of mobile operating licences, he said.
"The working group proposed that installation of the system must be completed within 90 days, but the NBTC board may consider whether the task can be done faster, as 60 days may be enough for installation," said Mr Prawit, who is also an advisor to the NBTC board chairman.
Such a system could be jointly developed by operators or by the NBTC office, he said.
The working group also agreed operators should add a "+" sign prefix for all incoming calls from overseas to allow people to reject incoming calls from abroad, said Mr Prawit.
Incoming calls from overseas could also be distinguished by prefixes, he said. For example, a +697 prefix could mean an incoming call from an unknown source overseas, while +698 could mean a call from someone using mobile numbers registered in Thailand, but using roaming services to call from overseas.
According to Mr Prawit, the operators said they needed time to rearrange their systems for the move.
"If people do not have family members or businesses linked with those in foreign countries, they should be careful in answering calls from overseas," he said.
The working group comprises representatives from 11 agencies: the NBTC, the Digital Economy and Society Ministry, the Personal Data Protection Committee, the Bank of Thailand, the Technology Crime Suppression Division, four mobile operators, the Telecommunications Association of Thailand under Royal Patronage, and the Consumer Organization Council.
Earlier this month, the NBTC board stepped up measures against mobile operators that allow the registration of more than five SIM cards by an individual through dealers by vowing to fine the carriers 1 million baht per day for violating the restriction.
The move is part of measures to address call centre scams and fraudulent SMS messages.