An international lawyer has appealed to US Immigration and Immigration and Customs Enforcement's (ICE) "moral authority" to reconsider deporting Irish man Keith Byrne.

In a letter to ICE, seen by RTÉ News, Michael Kingston argued Mr Byrne's deportation could traumatise at least six US citizens and asked that he be allowed remain in the country.

On Friday, Mr Kingston hand-delivered the letter to the offices of ICE Director Matthew Albence in Washington DC after Mr Byrne signed papers agreeing to leave the country.

Mr Byrne faced prison if he did not sign the documentation.

The lawyer called on the US to grant him a reprieve or a hearing with an immigration judge considering his "special circumstances".

Only in special circumstances can a deportation case be appealed and heard in front of an immigration judge.

Mr Kingston argued that Mr Byrne's family would be "spilt" if he was deported as he could not take his stepson, who "he treats as his own child", away from his biological father.

"Keith's family is going to be split up, traumatising these US children and his stepson's father and family. That includes at least six immediate US citizens," he said.

"He loves his stepson and would not take him away from his father, even if he was allowed to legally, nor would his mother, a US citizen who is now in an impossible situation if Keith is deported to Ireland."

Mr Kingston also pointed out that the Byrne family has made a huge contribution to the United States by leaving millions of dollars "to help the weak and needy".

Mr Byrne's great aunt Nellie Byrne married oil tycoon Ike West in San Antonio, Texas and donated $12.5 million to the Children's Hospital in San Antonio, where there is now a Nellie B West charity.

"Indeed, the United States owe the Byrne family some degree of recognition or even loyalty," he said.

Mr Kingston, from Goleen in Co Cork, said he heard Mr Byrne's "heartbroken" sister on local radio last week while on his way to the airport to travel to Washington DC on business and said he wanted to intervene.

After getting in contact with the Byrne family, he wrote the letter and also brought up Mr Byrne's case with US Senators on Capitol Hill, appealing to the "moral decency of the United States".

He acknowledged that Mr Byrne overstayed his original visitor's visa, which was "clearly wrong".

In the document, the 37-year-old was described as an "honest man" who attempted to mend his visa overstay and was open about his historic charges in Ireland.

"No one is above the law. That message still stands, and a firm message has been sent out, but nothing should ever prevent exceptional circumstances prevailing when moral authority rightly invokes their merit," Mr Kingston declared.

From Fermoy in Co Cork, Mr Byrne travelled to the US on a visa waiver programme in 2007, however, he overstayed his visa.

Two years later, he married American woman Keren Byrne and later became a father-of-three while establishing his own painting and decorating business in Oreland, Philadelphia.

Efforts to obtain a Green Card failed due to a minor drugs possession charge when he lived in Ireland.

He was arrested by officers two weeks ago on immigration violations and is currently being held at the Pike County Correctional facility.

Mr Byrne signed documentation last week, authorising his removal from the country. It is understood under the agreement he would banned from the US for five years.

"To grant Keith Byrne a reprieve allowing Green Card status, in his special circumstances, would enhance the moral power of this great nation and I have no doubt it will be repaid 100-fold in the same manner of Keith's great aunt, Nellie Byrne who contributed so magnificently in hard work, spirit, and financially, to the United States," Mr Kingston said.

In a statement to RTÉ News, ICE said that "per privacy restrictions" the agency cannot provide any further comment other than to state that Mr Byrne is currently in custody pending removal.