Rayong Refinery president Chainoi Puankosoom said the company had not yet consulted with the authorities on how to comply with the new rules but was ready to follow them, in order to reduce pollution in the area.

"If we receive official requests to reduce emissions to the air, we have options to follow, probably to import low-sulphur crude oil or install new equipment," he said.

"There would be a limited impact on existing plants that have earned environmental approval, but new investment that would come under tougher environment scrutiny would be affected."

The Pollution Control Department last week raised a proposal to make the Map Ta Put Industrial Estate an environmental-control zone. The estate houses a number of refineries and petrochemical plants.

PTT executive vice president Chitrapongse Kwangsukstith said the proposal required existing plants to install new technology to reduce emissions. From discussions with the authorities, it was determined that the private sector could be encouraged to do so through tax incentives.

Another PTT senior executive vice president, Prajya Phinyawat, said that before embarking on any move, the company would wait for clearer rules.

He said this should not affect existing plants but might affect new investment.

"Map Ta Put has been strategically planned to be an industrial area. If new investment cannot take place here, it would be a major issue for PTT. Right now, we are closely monitoring the development," Prajya said.

A BLCP Power source said the company's coal-fired power plant in the area could be a target for attack. However, he insisted  the plant had followed the government's emission standards strictly.