Democrat Party leader Abhisit Vejjajiva plans to seek a judicial review of the defence minister's move seeking to strip him of his military rank.
The opposition leader yesterday said he will have no choice but to file a complaint at the Administrative Court over the Defence Ministry's order to remove his rank.
The Democrats' legal team has been working on the draft petition, he said.
"I will use my rights and appeal the order [with the Administrative Court]," he said.
Mr Abhisit said he has been treated unfairly by an inquiry panel appointed by Defence Minister ACM Sukumpol Suwanatat to look into the matter.
He was accused of using a falsified military personnel registration document to apply for a job as a lecturer at Chulachomklao Royal Military Academy which, in turn, allowed him to be exempted from military conscription in 1987.
He said he did not have a chance to tell his side of the story when the committee wrapped up the probe and ruled to strip him of his rank and recall his salary.
He said the committee failed to be specific about the accusation he was supposed to answer and seemed in a rush to conclude the probe.
According to Mr Abhisit, he was invited to clarify a complaint that he improperly applied for a job with a state agency. He said the accusation should have been more specific.
The Democrat leader also said the defence minister had tried to mislead the public about the case by claiming it had to be sped up for submission to the Office of the Ombudsman.
He said the Office of the Ombudsman was not pressed for time to receive the report, "so using the Office of the Ombudsman as a reason to speed up the case is quite unusual".
Mr Abhisit also accused the government of double standards, citing a delay in the proposed stripping of the police rank of ousted prime minister Thaksin Shinawatra who was found guilty by the Supreme Court in the Ratchadaphisek land case.