Thailand’s telecoms regulator denied a request by dtac, the third-largest operator in the country, to temporarily continue using 850MHz spectrum it accesses under a concession while it migrates its 2G customers off the network.

The decision by the National Broadcasting and Telecommunications Commission (NBTC) means dtac has three days to migrate some 90,000 customers to other networks, as its 850MHz service will be cut off at midnight on 15 September. Customers roaming on the 850MHz band will also face service disruption.

Last week the operator filed a motion seeking to revoke a condition imposed by the NBTC preventing it from extending the use of the 850MHz band after the concession expires. It lodged a court petition seeking to protect its subscribers’ rights to use the network temporarily.

The regulator in July set a condition requiring the Telenor-owned operator to participate in a 900MHz auction if it wanted an extension to the concession period. Dtac opted not to participate in the auction and NBTC was forced to cancel the sale as other operators showed no interest.

NBTC secretary-general Takorn Tantasith said dtac was not granted additional time because the regulator did not consider the number of subscribers still using the 2G network as “substantial”, Bangkok Post reported. A condition of the 850MHz concession allowed dtac to extend its use of the frequency if a sufficient number of subscribers still used the network.

In addition, NBTC said dtac had the opportunity to acquire spectrum in the 900MHz band which would have enabled it run 850MHz services after an upgrade.

Chavit Sangudomlert, dtac’s head of investor relations, said in a statement it is waiting for a decision by the Central Administrative Court on the matter.