The Ombudsman has been asked to petition the Constitutional Court to rule whether the Thai-Cambodian memorandum of understanding (MoU) signed in 2001 on joint development in the Gulf of Thailand is in breach of the Thai constitution.
Palang Pracharath Party (PPRP) deputy leader Paiboon Nititawan made the request to the Office of the Ombudsman on Wednesday.
The 2001 MoU had not been approved by the Thai parliament before it was signed, which has resulted in it "having no legal effect from inception", according to Mr Paiboon's petition to the Ombudsman.
He named the Department of Treaties and Legal Affairs and the Ministry of Foreign Affairs as the first and second parties to be held responsible for what he believed was a breach of the constitution.
Mr Paiboon said that despite previously acknowledging that the MoU had not won parliamentary approval, the two parties continue using the MoU as a reference to what has been agreed by both nations regarding the 26,000km² of territorial waters in the Gulf of Thailand, which Thailand has sovereignty over.
The 2001 MoU is being referred to whenever the two countries try to reach further agreement on the possibility of sharing natural resources existing in these territorial waters, which are estimated to be worth more than 20 trillion baht, he said.
When the Ombudsman petitions the court to rule on this matter, Mr Paiboon said he requested that the Ombudsman ask the court to order the department and the ministry to stop using the 2001 MoU in its work pertaining to the demarcation of the territorial waters in question.
He said if the court rules the 2001 MoU to be unconstitutional and has no legal effect based on the grounds it was incomplete from the start, as stated in the 1969 Vienna Convention on the Law of Treaties, Thailand will be in a better position when fresh disputes over Thai-Cambodian overlapping claims arise.
He said Cambodia has always cited the 2001 MoU to back its position that Thailand had formally recognised these territorial waters as both nations' areas of overlapping claims.
Mr Paiboon also urged the Thai government to turn to the International Tribunal for the Law of the Sea in Hamburg, Germany, if the Cambodian government cannot agree that the 2001 MoU is invalid.