Caretaker Deputy Prime Minister Phumtham Wechayachai brushed aside claims that he is unfit to become defence minister because he joined the Communist Party of Thailand (CPT) in the 1970s.
Mr Phumtham, who became acting prime minister after Srettha Thavisin was dismissed by the Constitutional Court, has been tipped to become defence minister in the new Pheu Thai-led government.
This prompted former senator, Gen Somjate Boonthanom, to speak out against making the appointment.
"The government will appoint a big comrade, who fled into the forests in October 1976, to become defence minister overseeing military personnel," Gen Somjate posted on Facebook, referring to Mr Phumtham.
Mr Phumtham was among a group of students who fled into the jungle to join the CPT following the Oct 6, 1976 massacre of students and protesters at Thammasat University.
Responding to the criticism, Mr Phumtham said on Tuesday that it is up to Prime Minister Paetongtarn Shinawatra to decide which cabinet post he takes.
"But if I become defence minister, I want Gen Somjate to stop worrying. I went into the jungle to escape violent incidents that occurred in society at the time. I was not alone. There were students from other institutions who fled into the jungle," Mr Phumtham said.
Later, military leaders at the time decided to adopt a reconciliatory approach to open the way for students and others who supported the CPT to return to society, Mr Phumtham said.
He referred to Prime Minister’s Order 66/23, which was introduced by the government of Gen Prem Tinsulanonda in 1980, to allow those who joined the CPT to reintegrate into society and join a national development programme aimed at rehabilitating them.
"Since then, I have never been involved in any activity [related to the CPT]. I have proven myself during the past 50 years. I always put the people's best interests first," Mr Phumtham said.
"I am not in conflict with anyone. I believe in the good intentions of everyone, particularly the military. If I become defence minister, I will do everything in my power to ensure the military stay by the people's side and help them in difficult times," he said.