The Stop Global Warming Association Thailand will seek to nullify the cabinet's approval of the construction of Mae Wong Dam in Kamphaeng Phet province by filing a complaint today to the Central Administrative Court.
The NGO's complaint, supported by about 160 environmental protection groups, will be filed against Prime Minister Yingluck Shinawatra, the cabinet, the Minister of Agriculture and Cooperatives and the director-general of the Royal Irrigation Department.
They have been accused of violating the constitution.
Srisuwan Janya, the association's president, said the cabinet agreed in principle on April 10 to the construction of Mae Wong Dam, despite the project needing to pass an Environmental and Health Impact Assessment (EHIA) first.
Dam construction is among 11 harmful projects that require an EHIA study and a comment from the Independent Commission on Environment and Health, according to Section 67 of the constitution.
"We have received a lot of proof confirming that the project has already been approved by various agencies," Mr Srisuwan said.
"The cabinet has also approved it without an EHIA study, which is required by the law. They have already done something against the law."
Mae Wong Dam is among 21 dams that are part of the government's flood management scheme, which has an overall budget of over 350 billion baht.
If the dam is constructed, 13,260 rai of fertile forest inside the Mae Wong National Park will be inundated.
The area is a part of the Thongyai-Huai Kha Khaeng Wildlife Sanctuaries, a Unesco world heritage site.
The government said the project will help locals survive drought and ease their suffering from flooding. The Royal Irrigation Department expects to complete the EHIA this month.
Sasin Chalermlap, secretary-general of the Sueb Nakhasathien Foundation, which is one of the supporting plaintiffs, said legal action against the government is the only way to stop the project.
"We do not see any effective way to stop the project except through the court," Mr Sasin said.
"It is clear that the government's decision to go ahead with the project was made without any consideration of the environmental impacts."
Mr Srisuwan said he has submitted a letter to Science and Technology Minister Plodprasop Suraswadi, in his capacity as chairman of the Water and Flood Management Committee, demanding the government stop its 350-billion-baht flood prevention scheme.
He said the government is acting against the constitution by approving the massive budget without the people's participation.
"If we do not receive any reply from Mr Plodprasop within 90 days, we will again file a complaint to the court against the government's 350-billion-baht flood management scheme," Mr Srisuwan said.
The Stop Global Warming Association Thailand has filed a complaint with the Administrative Court in over 50 cases on environmental conflicts.
It won one case regarding Map Ta Phut projects, when the court agreed to postpone the expansion of petrochemical projects in Map Ta Phut industrial estate in Rayong.