Businessman Denis O'Brien has berated Social Protection Minister Joan Burton for questioning his appearance in public with government figures.
In a stinging letter, the billionaire who was criticised by the Moriarty tribunal accused Ms Burton of "vindictiveness" and of making a "startling" personal attack on him.
Mr O'Brien also criticised her Labour Party colleague, Public Expenditure and Reform Minister Brendan Howlin, for endorsing her comments, accusing him of "political opportunism".
Ms Burton is the second government minister to have received a letter of complaint from Mr O'Brien in the aftermath of his appearance on the New York Stock Exchange alongside Taoiseach Enda Kenny last March. Mr O'Brien also wrote to Lucinda Creighton -- but the tone of his letter to Ms Burton -- disclosed for the first time today -- is harsher.
"I recognise that your political persuasion naturally leaves you unsympathetic towards someone in my position, but I remain concerned at the level of vindictiveness underpinning your remarks," he wrote.
"That your comments would be endorsed in quick time by your party colleague, Minister Brendan Howlin TD, was an unsurprising display of political opportunism.
"I, clearly, am undeserving of any semblance of fair or balanced treatment. Political expediency demands outright condemnation. It is the easy option."
The letter was sent to Ms Burton's ministerial office on April 4, a week after she spoke of "considerable public and political unease" about the fact that Mr O'Brien "continued to pop up" at various public events despite the adverse findings of the Moriarty tribunal.
Mr O'Brien's appearance at a bell-ringing ceremony at the New York Stock Exchange (NYSE) alongside Mr Kenny caused much public comment.
Both men were there for a conference to coincide with St Patrick's Day. Their appearance together coincided with the first anniversary of the publication of the Moriarty tribunal report.
That report concluded that Michael Lowry, the ex-Fine Gael minister, helped Mr O'Brien to win the lucrative mobile phone licence and that Mr Lowry had received payments from Mr O'Brien.
Speaking in the Dail after the bell-ringing ceremony, Ms Burton told the Dail that "it is perhaps time for the Government to reflect on how it should in future interact with people against whom adverse findings have been made by tribunals".
In his letter to Ms Burton, Mr O'Brien wrote: "I am not a convicted criminal. I have never been charged with a criminal act. For someone with a proud record of defending the civil and constitutional rights of the individual in Ireland (as you undoubtedly have), your personal attack on me is all the more startling."
He criticised the Moriarty tribunal's conclusions as unsound, a violation, and rejected its findings: "I did not make any payment to Mr Michael Lowry TD. Esat Digifone won the second mobile phone licence competition process because it submitted the best bid," he wrote to Ms Burton.
Mr O'Brien also took issue with something Ms Burton had said about him on television "several years" ago. "You accused me of benefiting from a state licence and making vast amounts of money, which was incorrect," he wrote.
"I felt that I ought to write to you to voice my concerns. Indeed, I would welcome an opportunity to meet you to explain my position more comprehensively."
However, Mr O'Brien concluded his letter by thanking Ms Burton for her "warm greeting" at the NYSE. "I think showing a united front when overseas is one of the great hallmarks of the Irish."
This was a reference to a brief encounter with Ms Burton -- who also attended the conference at the NYSE but not the bell-ringing ceremony -- as they passed each other.
The letter to Ms Burton was released under the Freedom of Information Act.
Ms Burton declined to comment this weekend while a spokesman for Mr O'Brien did not provide a comment.