A letter from the American Ireland Fund to Democratic and Republican leaders in the house outlined their annoyance.
The letter, signed by New York hotelier John Fitzpatrick, was sent two days before the Senate finally approved President Obama’s nominee Kevin O’Malley.
The letter urged the Senate to confirm the new ambassador to Ireland and end a record delay in filling the role.
Two days later Kevin O’Malley, a lawyer from St Louis was appointed.
Confirmation of his appointment ended a 21-month period without an American ambassador in Dublin, the longest period that the post has been left vacant since Washington first appointed a diplomatic envoy to Ireland in 1927.
American Ireland Fund chairman Fitzpatrick wrote to Harry Reid, the Democratic majority leader of the senate, and Mitch McConnell, the Republican minority leader of the chamber.
He said: “I write to you on a matter of great concern to Ireland and Irish America, namely the appointment of an American Ambassador to Ireland.
“To many of us here and back in Ireland it is a matter of great bewilderment and not just a little annoyance that the post of ambassador has remained unfilled for so long.
“This is unprecedented in Irish-American relations and undoubtedly, in the case of two such close nations.”
Fitzpatrick confirmed that the fund was aware that the issue of the appointment of ambassador was due to be discussed by the Senate that week.The Irish Times reports that he urged the two Senate leaders ‘to use your influence to reach a successful conclusion to these discussions.’
He added: “At a time when our trading relations are so crucial, uncertainty besets the Northern Ireland Peace Process and great changes are occurring in the European Union, it would be reprehensible were this pivotal post to remain open for any longer.”
The American Ireland fund has raised about $500 million for charities and other causes on the island of Ireland.
It is widely regarded as one of the most politically connected Irish-American groups in the United States.
New ambassador O’Malley, a long-time supporter of President Obama, is a grandson of emigrants from Westport in County Mayo.
A former federal prosecutor, he is the 27th US Ambassador or envoy to Ireland and the first to be appointed from Missouri.
The previous ambassador was Irish-American businessman Dan Rooney, who stood down in December 2012.