The petition, signed by 67 senators, was accepted yesterday by Surachai Liangboonlertchai, the first deputy speaker.
Paiboon Nititawan, a senator in the Group of 40, said the G-to-G contracts to sell 7.32 million tonnes of rice worth more than 114 billion baht concerned the country's trade and investment. They might affect economic security by incurring public debt, potentially causing a financial crisis, he added.
The senator said the G-to-G sale contracts might require parliamentary approval under Section 190, because they could affect all citizens of the country.
He also said a Senate committee had inquired about the details of G-to-G rice sales but a deputy director-general of the Department of Foreign Trade had refused to provide the information, insisting the G-to-G deals were confidential.
Mr Paiboon urged greater government transparency.
He warned that the government's rice-pledging scheme could lead to excessive rice stocks being held in storage. Over time, the quality of the warehoused rice could decline, affecting the strong brand image of Thai rice worldwide.
Mr Surachai said he would first verify the documents, including the names of the senators, before forwarding the petition to the Constitution Court.
Democrat Party leader Abhisit Vejjajiva called on the government to change the subsidy method by allocating about 150 billion baht expected to be lost from rice pledging to farmers directly so that state money would actually reach them.
"I'm not being sarcastic. It's based on economic principles. With direct allocation of the money, many more farmers would reap benefits and the money would not be split up into the hands of traders and millers," he said.
Democrat MP Warong Detwikrom complained yesterday that farmers received only 10,500-11,000 baht per tonne from pledging their rice, not the 15,000 baht per tonne claimed by the government.
He also said that farmers were complaining about delayed payments under the pledging scheme.
The opposition MP added that Thailand has exported only 5 million tonnes of rice so far this year. He said the country exported 9 million tonnes of rice during the same period last year, meaning exports had plunged by 44%.
Meanwhile, Pol Maj Gen Jakthip Holasutsakul, deputy commissioner of Region 3 Provincial Police, said police have charged the management of Tanyarungroengchai Rice Mill Co with fraud after more than 10,000 tonnes of pledged rice worth over 200 million baht disappeared from its rice mill in Muang district of Nakhon Ratchasima.
Police also found the names of 460 farmers had been used illegally to seek money from the rice-pledging scheme in Nong Ki district of Buri Ram province.