The licence for the 900 MHz spectrum is likely to have a reserve price of 37.9 billion baht ($1.15 billion), the regulator has said, based on the previous auction.

AIS, owned by Singapore-based SingTel, said in a statement that it would not participate after taking into consideration the terms of the auction. AIS did not elaborate.

True, Thailand's second largest mobile operator, said that it would also skip the 900 MHz auction.

Total Access Communication Pcl, the country's No. 3 operator, has yet to say if it will join the auction.

The National Broadcasting Telecommunications Commission (NBTC) has scheduled the auction for Oct. 20, but said it would be delayed to Oct. 28 if there was only one participant.

In August, AIS and DTAC, each won a band on the 1800 MHz spectrum for 12.5 billion baht per licence.

(Reporting by Chayut Setboonsarng; Editing by Himani Sarkar and Darren Schuettler)