PTT Plc is in the process of laying a 28-inch pipeline four metres below ground level alongside the Asia Road from Ayutthaya to Nonthaburi and from Ayutthaya to Nakhon Sawan.
The pipeline will carry natural gas for vehicles (NGV).
Land is subsiding in tambon Kunglan between the 13km and 14km markers of the road.
A Chinese firm is handling the job. The company has allegedly barred both Thai and Chinese workers from speaking to the media.
However, a number of Thai workers have warned the company is failing to insert steel sheeting far enough into the ground to prevent the subsidence.
Workers have been told to place steel sheet piles between four and six metres into the ground, but say the sheeting should go down for at least 10 metres to prevent the land from subsiding.
They warned the Chinese engineers have refused to suspend construction for an inspection, despite the fact the subsidence is clearly visible. The Thai workers said they are worried about their safety if the work continues without corrective measures.
Local business owner Suchart Manit said one of his temporary buildings had been cracked as a result of the subsidence. He urged the Chinese contractor to take responsibility for his assets and the other buildings that have been damaged in the construction of the pipeline.
Mr Suchart, who runs construction company Sor. Theptipong, agreed that the steel sheet pile being used in the project was insufficient to prevent subsidence.