CAT Telecom's labour union says it will file a petition with the Central Administrative Court today against the telecom regulator over Wednesday's 1800-megahertz spectrum auctions if its board fails to do so.
"If the management do not secure approval from the board members by today, we will move to sue the National Broadcasting and Telecommunications Commission [NBTC] ourselves," said Sungvorn Poomtian, president of the labour union.
"We don't want to set the country back. We just want to reserve the right to protect our organisation's benefits."
The NBTC has set the auction for two licences of the 1800-MHz spectrum on Wednesday, with each containing 15 MHz of bandwidth.
Mr Sungvorn said the NBTC has no authority to auction the 30 MHz of the 1800-MHz spectrum because CAT was awarded the right to hold the entire 75-MHz bandwidth of the frequency until 2025 by the now-defunct National Telecommunications Commission.
CAT awarded 50 MHz of bandwidth on the 1800-MHz spectrum to Total Access Communication Plc (DTAC) to provide 2G mobile service under a concession agreement, which is due to expire in 2018.
Another 25 MHz of bandwidth on the 1800-MHz spectrum was awarded to TrueMove and Digital Phone Co under a concession agreement with CAT. Both concessions expired in September 2013.
"We [CAT] should have the right to use the whole bandwidth of the 1800-MHz spectrum at least until 2018 after DTAC's concession expires," said Mr Sungvorn.
He said CAT's licence was awarded before other laws, including the Telecom Business Act of 2001 and the Frequency Allocation Act of 2010, took effect.
Therefore, CAT's licence agreement should be valid until 2025, said Mr Sungvorn.
CAT acting president Col Sanpachai Huvananda declined to elaborate if CAT's management will take legal action against the NBTC before the auction date.
TOT Plc's labour union also filed a petition at the Central Administrative Court last week against the NBTC's 900-MHz spectrum auctions.
The regulator plans to auction two licences of the 900-MHz spectrum on Dec 15, each containing 10 MHz of bandwidth.
The 900-MHz spectrum was previously used by Advanced Info Service under a concession agreement with TOT, which expired in September.
Under the NBTC's law, after the expiry of a concession spectrum must be reallocated through auction.