With a tepid automobile market, the five existing eco-car makers are finding it hard to honour the requirements imposed in the first phase, which calls for them to make 100,000 vehicles a year each.
Board of Investment (BoI) regulations stipulate each car maker must manufacture a minimum of 100,000 eco-cars annually from the fifth to the eighth years after kicking off production.
Thailand embarked on the first phase of the eco-car scheme in 2007, drawing five manufacturers -- Nissan, Honda, Mitsubishi, Suzuki and Toyota.
Nissan last year became the first to start making 100,000 eco-cars, with Honda scheduled to fulfil the figure this year.
Mitsubishi and Suzuki are due to make 100,000 next year, while Toyota expects to follow suit in 2017.
Kazutaka Nambu, president of Nissan Motor (Thailand), admitted his company was now increasingly concerned that its eco-car production might miss 100,000 vehicles this year, saying the sales of two models -- the March and the Almera -- had declined sharply this year.
It sold only 8,121 eco-cars from January-June, down by 20% year-on-year.
Last year the March and the Almera together accounted for 21,603 vehicles sold, down sharply by 63.8%.
Mr Nambu said Nissan was planning to increase eco-car production volume for shipment from the current 50% to 70% in the near future.
International destinations are Oceania and Asia including Japan.
"The export volume will hopefully help to offset sluggish local sales," Mr Nambu said.
Takayuki Sugiyama, president of Suzuki Motor (Thailand), said his company had to launch new models to fulfil the minimum production requirement next year.
He is upbeat that production of three eco-car models -- the Swift, the Celerio and the Ciaz -- could hit a total 100,000 vehicles this year, mainly for export.
Suzuki sold 8,737 eco-cars locally in the first half, down by 6.2% year-on-year, and exported 19,409 in the same period, a hefty increase of 664%.
"Suzuki is committed to exporting 40,000 eco-cars this year, up by 285%, of which the Celerio will be exported to Europe and the Swift to Asia, while markets for the new Ciaz are being considered," Mr Sugiyama said.
Mr Sugiyama said if production of the three models failed to reach 100,000, Suzuki would introduce a new model in order to meet BoI requirements.
At present, Toyota controls 34.6% of the eco-car market, followed by Suzuki (16.3%), Nissan (16%), Mitsubishi (15.5%), Mazda (14.16%) and Honda (3.5%).