The Constitutional Court has given caretaker Prime Minister Yingluck Shinawatra 15 days to defend a controversial cabinet decision to remove Thawil Pliensri from the position of National Security Council (NSC) secretary-general.
The future of her tenure as caretaker prime minister, and of her cabinet, hangs on the court's decision.
The 15-day timeline was set after the Constitutional Court unanimously accepted for consideration a petition filed by 28 senators arguing that Ms Yingluck's order for the removal of Mr Thawil on Sept 30, 2011 was in violation of sections 182 (7) and 268 of the constitution.
The Constitutional Court said Ms Yingluck must explain the decision to the court within 15 days of it receiving the full documentation supporting the petition.
Under the law, if the Constitutional Court rules against her, she and the entire caretaker cabinet would have to leave office.
"All cabinet ministers have to go if the prime minister is disqualified," Senator Somchai Sawaengkarn told FM101 radio station on Wednesday.
The petition filed by the 28 senators, led by Paiboon Nititawan, is based on the Supreme Administrative Court ruling on March 7 that the transfer of Mr Thawil to the position of prime minister's adviser was unlawful and it was made for the benefit of the prime minister.
The Supreme Administrative Court ordered his reinistatement as NSC chief.
Mr Somchai, a signatory to the petition, said the documents will be forwarded to the Constitutional Court as soon as possible.
The senator was confident of winning the case. "The transfer order was clearly made to benefit the prime minister," he said.
The petitioners will submit to the court documents supporting their case of a link between the removal of Mr Thawil from the NSC secretary-general's position and the subsequent appointment of Pol Gen Priewphan Damapong, Ms Yingluck's brother-in-law, as police chief, he said.
Mr Thawil was transferred to clear the way for then police chief Pol Gen Wichien Potephosree's appointment as his replacement at the NSC, Mr Somchai said.
Pol Gen Priewphan was then promoted from being one of several deputy police chiefs to be Pol Gen Wichien's successor as national police chief, he said.
Pheu Thai Party members came out to attack the Constitutional Court, saying the decision to accept the petition for consideration had long been expected.
Pheu Thai Party leader Charupong Ruangsuwan and party spokesman Anusorn Iamsa-ard both said the NACC and the court were determined to unseat the government and warned that their credibility was in jeopardy.
"The NACC and the court are taking power away from people who gave their mandate to the government," Mr Charupong said.
Mr Anusorn said the transfer of Mr Thawil was a normal process. The Thawil case was aimed at unseating the government, he added.
If the court rules against Ms Yingluck it would set a precedent barring future governments from moving government officials to other jobs, he said.
Ms Yingluck is also fighting allegations by the NACC that as chair of the National Rice Policy Committee she negligently failed to stop corruption and financial losses incurred in the governent's flagship rice-pledging scheme.