Thailand’s telecoms regulator has rejected the agreement between state-owned CAT Telecom and dtac for the latter to return 5MHz of unused spectrum because it wants to avoid any possible delay in the 4G auctions at the end of the year.

After years of negotiations, CAT agreed just two days ago to allow dtac to return 5MHz of unused 1.8GHz spectrum to the National Broadcasting and Telecommunications Commission (NBTC).

The country’s long-awaited 4G auctions, delayed by more than a year since the military coup a year ago, are planned for November and December.

Two slots of 12.5MHz in the 1.8GHz band are scheduled to be sold off. The return of the 5MHz would increase the amount to 30MHz, which could be divided into two 15MHz blocks to better maximise use of the airwaves.

NBTC secretary-general Takorn Tantasith said it hasn’t been officially notified by either party, the Bangkok Post reported. “We don’t want to take a risk, as we don’t want to face any further delays.”

The latest twist comes after the so-called NBTC superboard (a special committee set up to evaluate the performance of the regulator) asked for the auctions to be delayed since operators have complained they each need at least 20MHz to offer 4G service effectively. The ICT minister also recommended last month that the country’s state-owned operators and broadcasters return their used spectrum so it can be refarmed and auctioned as 4G spectrum.

Takorn, who announced on Tuesday he will resign on 1 September, said his departure will not affect the auction schedule, the Post said.