Phirakan Kaeowongwattana said on Thursday he was consulting his lawyers to file criminal and civil lawsuits against Chamroon Tangpaisalkit, the firm's board chairman, and reiterated that personal conflicts and his attempt to crack down on corruption in the company were behind his contract termination.
The board fired Mr Phirakan on April 9 after 11 months in office after an internal probe found that he had presented fake documents when applying for the position.
He was the first managing director of the firm, which operates the Airport Rail Link connecting Bangkok and Suvarnabhumi airport.
"I learned of the contract termination from the press. I should have been informed about it 30 days in advance and should have had a chance to hand over my job to limit the damage to the company,'' he said.
But he said he was blocked from entering the company for a job handover by security guards.
He planned to seek fairness from caretaker Transport Minister Chadchart Sittipunt.
SRT Electric Train Co issued a press release on Thursday quoting him as saying that he was determined to continue working in the position and rejected the board decision to sack him.
"First of all, I would like to tell all of you that I will continue in my job and confirm the plan to improve the organisation as I promised all staff on the first day that I took up the job,'' he said in the press release obtained by the Bangkok Post.
Mr Phirakan said earlier that he was fired after he complained about some of Mr Chamroon's procurement projects and the employment of Mr Chamroon's young relatives at the company.
Mr Phirakan claimed he found irregularities in some acquisition contracts.
Mr Chamroon on Thursday ignored the threat and confirmed that the dismissal decision was properly taken by all board members who unanimously agreed on the issue. The former Airport Rail Link chief had the right to take legal action, he added.
The decision to fire him has been officially reported to the State Railway of Thailand, which holds a majority stake in the firm, the Transport Ministry and the Finance Ministry, the board chairman said.
The board will make a decision at its next meeting to demand Mr Phirakan pay back the salary he has been paid, he added.
Mr Chadchart said the conflict involving Mr Phirakan's dismissal rested with the board, but said he would ensure fairness to all sides.