NBTC secretary-general Takorn Tantasit insisted there would be no further delays to the auction.
Former president of the Thailand Telecommunication Management Academy, Anuparp Thiralarp, has threatened to petition the Administrative Court to suspend the auction until the agency amends its regulations to "better benefit the public in compliance with the constitution".
Mr Takorn said Mr Anuparp's threat to take legal action today came as no surprise _ five other people have already lodged a slate of legal challenges to halt the auction.
The NBTC plans to auction off the 2100 megahertz bandwith on Oct 16 for use with 3G technology.
Three main private mobile operators _ Advanced Info Service (AIS), Dtac and True Move _ are expected to bid for the licences.
The NBTC will announce the names of the qualified bidders Tuesday. Disqualified applicants will have three days to appeal.
Mr Takorn said the auction procedures have been carried out under the 2010 Frequency Allocation Act.
"We're now ready to clarify all questions concerning the 3G auction process and regulations," he added.
Mr Takorn said the 3G licensing auction procedure is legally binding and covers all possible concerns, including service quality standards, technology development and consumer protection.
Mr Takorn said the NBTC will transfer tens of billions of baht from the sale of the 3G spectrum to the Finance Ministry to invest in other public services.
Opponents of the auction have called on the NBTC to revise the bid terms. One demand is that the NBTC should limit service charges for 3G mobile services at 200 baht a month.
Mr Takorn said he expected that the 3G service will come with lower prices than existing rates because operators will enjoy lower operating costs under the new licensing system.
3G operators will be subject to a licensing fee of 2% of their annual revenues and a 3.75% universal service obligation tax on the revenue.
He said the NBTC plans to draft a new regulation establishing a ceiling for mobile phone service charges. The new rate will be lower than the existing rate of 99 satang per minute.
NBTC commissioner Suthiphon Thaveechaiyagarn warned that Mr Anuparp, who is threatening to sue in order to stop the auction from going ahead, should check the law properly before filing his petition.
Mr Suthiphon said the 3G licence auction is clearly covered by Section 45 of the the Frequency Allocation Act, the Telecommunications Act as well as the constitution.
Mr Anuparp claims the NBTC has not allowed for regulating the prices charged by operators for data transmission, a loophole that could result in licence holders increasing data charges at the expense of consumers.
Songkhla Wichaikhatkha, a legal adviser to the NBTC, said that even after the winner is selected, 3G services cannot be launched straight away because an operator must build at least 80% of its network before offering the service to customers.
When the NBTC knows how much it costs to build the network then it will set rate ceilings, he said.