"However, I have not yet received petitions submitted by homebuyers over the issue," he said, admitting that subcontractors hired by the NHA to collect service bills might have overcharged customers.

Phornsak said he had also been aware of subcontractors "forcing" homebuyers to use only their service and materials for renovation work by lying to them that a renovation licence would not be granted unless the subcontractors' materials were used.

He said the problem had occurred because too many Ua Athorn projects were being implemented.

"The NHA cannot oversee them all thoroughly and therefore these subcontractors have been hired [by local NHA officials] to assist in collecting service bills," he added.

Residents of an Ua Athorn housing project at Rangsit had earlier petitioned the Assets Examination Committee (AEC) to investigate irregularities in the awarding of the construction contracts and the suspicious repossession of houses sold.

Phornsak said an initial finding showed there were more than 10 subcontractors fooling homebuyers to use their services for renovation. He said he would report the incidents to the AEC and then seek legal action to terminate contracts with those subcontractors.

NHA deputy governor Thitanont Phiboolnakharin said around 8,000 Ua Athorn homebuyers, out of a total of around 200,000, had not yet paid water or electricity bills and had received warning statements from subcontractors.

Most of those who submitted petitions to the AEC said they had been treated unfairly by the subcontractors as their warning statements threatened repossession of their homes unless they completely covered the bills.