All extraditions from the UK to the Republic of Ireland should be suspended amid uncertainty over Dublin's position on handovers post-Brexit, the High Court in Belfast heard today.
Judges were told Irish authorities wanted to "have their cake and eat it" by seeking a man charged with benefit fraud while staying requests for people wanted in Britain.
Ronan Lavery QC claimed it amounted to a breakdown of the principle of mutual recognition within the European Union.
Insisting the extradition process must be a "two-way street", he argued: "The UK has to set down a marker in relation to this case with Ireland, or else all of the other EU member states will be at this as well."
His client, Enda Toner, from Cullyhanna in south Armagh, is appealing an order for his extradition to the Irish Republic.
Toner is being sought in connection with 165 allegedly fraudulent job seekers allowance claims worth around 34,000 euros.
Detained in Northern Ireland on a European Arrest Warrant last December, he remains in custody pending the outcome of his legal challenge.
Lawyers for the requested person centred their appeal on a decision by Ireland's Supreme Court earlier this year to refer a separate extradition request from UK authorities to the European Court of Justice.
Thomas Joseph O'Connor, 51, of Cloughbeirne, The Walk, Roscommon, is wanted over a £5 million pound tax fraud.
With O'Connor claiming extradition could violate his rights as an EU citizen because of the UK's decision to leave the Union in March 2019, legal clarity is urgently being sought from Luxembourg.
Up to 20 extradition cases to the UK remain held up, pending the outcome of the referral.
But according to Mr Lavery the Irish authorities are refusing to cooperate with extradition requests.
"The principle of mutual recognition has been suspended, it's broken down," he contended.
"One country isn't playing ball and there's no reason why we should extradite our citizens to that country.
"They don't want to extradite to the UK yet they want us to extradite to the south, they want to have their cake and eat it."
Asked by Lord Justice Treacy if he meant the UK should not extradite anybody to the Republic of Ireland, the barrister replied: "Yes - not while this is pending.
"This is a two-way street where we have an extradition treaty with the Republic of Ireland on the basis of reciprocity."
Referring to the decision taken in O'Connor's case, he insisted: "The Irish Supreme Court knew exactly what it was doing, and it knew what the potential effect of this might be."
Stephen Ritchie, representing the authorities in Dublin, countered that there is no legal impediment to Toner's extradition.
He added: "It's not a lack of cooperation or refusal, what the Republic of Ireland is doing is asking for direction from the European Court of Justice on this point."
Reserving judgment on the appeal, Lord Justice Treacy pledged to give a decision within weeks.