The National Broadcasting and Telecommunications Commission (NBTC) has begun investigating whether tariff plans for third-generation (3G) mobile services by the three main operators comply with price regulations.
The watchdog imposed a regulation requiring the operators - subsidiaries of Advanced Info Service (AIS), Total Access Communication (DTAC) and True Move - to cut tariffs for 3G service packages by 15-20% from the existing 2G service rates as of last Dec 7.
But the NBTC does not require all 3G tariff packages to comply with the regulations, saying customers have a right to choose from various tariff plans.
Vice secretary-general Korkij Danchaivichit said the NBTC has started collecting operators' daily promotional tariff packages from all media channels.
Though a serious examination begins next week, he admitted it would be too early to conclude whether all operators' packages complied with the rules.
"We need to wait for one month to calculate an average price," said Mr Korkij.
He warned that operators failing to comply could face penalties ranging from a warning to licence revocation.
The NBTC is also drafting a regulation governing the maximum tariff for both voice and data use, which is expected to be ready next month, said Mr Korkij.
The current regulation covering only the voice tariff requires operators to charge no more than 99 satang a minute.
The three operators and TOT on Thursday initially agreed to enter into a new agreement on the interconnection charge for mobile services.
The new rate will be 45 satang a minute for both 3G and 2G service, effective June 1.
The interconnection charge is what the networks of callers must pay the networks of receivers.