All airlines holding air operating licences must submit shareholding details to the Civil Aviation Authority of Thailand (CAAT) by Jan 20 or face licence revocation.
CAAT director Chula Sukmanop said the requirement is part of the agency's tightened rules on the aviation industry to ensure Thai nationals are not being used as fronts for foreign interests.
The law caps foreign ownership of local airlines at 49%. In addition, two thirds of the board of directors on the airlines must be Thai.
Each airline is also required to reveal its Thai shareholders give details of sources of registered capital to ensure it is not controlled by foreign investors.
A total of 48 airlines that were granted licences must submit the information to the CAAT for examination by the deadline otherwise their licences will be revoked, he said.
An air operating licence (AOL) is a prerequisite to apply for an air operator certificate (AOC).
Mr Chula said three more airlines - Asia Atlantic Airlines, Siam Land Flying and AC Aviation - had qualified to receive AOLs pending approval from Transport Minister Arkhom Termpittayapaisith. Two applications for AOLs are expected to be forwarded to the CAAT board for consideration on Dec 23.
According to the CAAT director, the agency is also asking the airlines with AOLs to apply for AOCs. Applications were open from yesterday.
Of 21 airlines, 13 have been reissued AOCs, he said, adding that more airlines are likely to be granted them within this month and the rest by January next year.
He said the country's aviation industry is expected to grow by 5.8% next year following the recent lifting of the red flag by the International Civil Aviation Organisation (ICAO).
He said the robust tourism sector and the removal of the red flag were key factors helping to drive the aviation industry and competitiveness.
Although lifting the red flag was a significant turning point for the aviation industry, Thailand and the CAAT must carry on their mission to improve aviation safety standards, said Mr Chula.
But Thailand's reputation will only be fully restored when the the US Federal Aviation Administration (FAA) returns the nation to Category I status. Currently demoted to Category II, restrictions remain on operations by Thai-registered airlines to the US, he said.
Mr Chula also said the CAAT plans to ask the FAA to audit in February next year to seek the upgrade of Thailand's aviation industry's status.
However, the industry's current status is seen as reflecting reality as there are no Thai-registered airlines serving the US.
The FAA downgraded Thailand to Category II status after the ICAO placed a red flag on Thailand.
CAAT officials said in October they would initiate the process to have the FAA audit Thai aviation standards in the first quarter of next year.