The Foundation for Consumers has demanded authorities protect the rights of customers affected by Thai Airways International (THAI)'s financial woes.
Narumon Mekborisut, head of the foundation's consumer rights protection unit, said customers outside of the country also need help.
Many customers were reportedly facing a delay of up to six months in getting ticket refunds from the airline.
The customers were also offered remedial options of postponing travel dates with no extra charge, extending the tickets' validity, and exchanging the tickets for travel vouchers of equal value, according to THAI.
Ms Narumon said the foundation has written to the Transport Ministry and the Civil Aviation Authority of Thailand asking them to look after any customers who might be unfairly treated in exercising their options offered by the airline.
THAI has entered a pre-phase of debt rehabilitation after the Central Bankruptcy Court accepted its rehab petition for examination on Wednesday.
Ms Narumon said the airline must spell out refund deadlines. For example, she said, a cash refund should not take more than seven days.
THAI has said it needs up to six months to refund customers due to the court proceedings and obligation under the bankruptcy law. It is not known how many customers are affected by the potential delays.
Other commercial airlines registered in Thailand have also sought soft loans from the government to prop up their businesses.
However, Ms Narumon said the airlines should not secure funds until they have dealt with issues concerning refunds.
