US billionaire Donald Trump has strongly warned the Taoiseach against selling the State's shareholding in Aer Lingus, claiming it would damage the country's tourism industry and links to foreign direct investment.
Mr Trump, who is considering a run for the White House, insists the airline provides "strategic advantages" to Ireland and "should not be given away to the highest bidder".
The high-profile businessman claims IAG boss Willie Walsh has the interest of shareholders as his "number one priority", adding: "I do not think this is a good deal for Ireland."
Significantly, Mr Trump indicates that protecting the State's shareholding in Aer Lingus is important to his plans to further invest "many millions of dollars" in his hotel and golf resort in Doonbeg, Co Clare.
"Aer Lingus, like the Irish shamrock and Guinness, is essentially Irish with a strong national identity which is very important to your country. It should not be given away to the highest bidder," Mr Trump wrote.
"Aer Lingus is a brand that you and your country should be very proud of. It is much more than a business transaction," he added.
The decision by the high-profile businessman to wade into the row over the future of Aer Lingus comes as negotiations enter their most crucial phase.
And it comes after the Richard Branson-owned airline, Virgin Atlantic, claimed the sale of the State's 25.1pc stake would jeopardise competition and result in increased ticket prices.
Mr Trump's warning is made in a letter sent personally to Enda Kenny last month, which has been obtained by the Irish Independent.
The letter was also sent to Transport Minister Paschal Donohoe and Finance Minister Michael Noonan, who personally welcomed Mr Trump at his arrival at Shannon Airport in May.
Mr Trump has made a significant investment in his Co Clare resort, which employs over 250 people during peak season.
In his two-page letter to the Taoiseach, the boss on TV show 'The Apprentice' says the Heathrow slots provide the country with a strategic advantage that is "immeasurable".
"An island nation that depends so heavily on tourism, foreign direct investment and business links needs as much advantage as it possibly can get.
"Shannon Airport has begun to grow its numbers over the last number of years and it needs time to make its contribution to the economy of the West of Ireland, of which I know you are a proud citizen," he wrote.
And he specifically mentions his plans to invest further in Doonbeg.
"The tourism initiative of The Gathering in 2013 was terrific and more importantly The Wild Atlantic Way is a fantastic idea.
"Please allow them time to prosper while maintaining control of your national airline and the strategic advantages it provides to your nation," he said.
"For my own part, I am incredibly proud of Trump International Golf Links & Hotel, Doonbeg, Ireland, a jewel in Irish tourism and one that has great future potential to impact the local economy over the next number of years. I want to protect this business, its jobs and, of course, my own investment.
"With that in mind, may I urge you not to sell your Government's share in Aer Lingus to IAG. I know you will make the right decision."
While support for a deal is growing within Fine Gael, a cohort of Labour TDs insist they still have serious concerns.