A Polish national challenging the enforcement in Northern Ireland of child maintenance orders from his native country is set to take his fight to the European Court of Justice.
Lawyers for the man contend payment decisions cannot be applied because they were made before Poland joined the EU.
Judges in Belfast have rejected claims that the regulations have no retrospective force beyond the point at which the country obtained membership.
But the case is now going to be appealed further in an attempt to clarify an issue with potentially far-reaching consequences.
Solicitor Conal McGarrity of PA Duffy and Company said: "This is a landmark case involving a point of EU law that is currently without precedent, meaning that it has now been successfully referred to the European Court of Justice for a decision.
"The outcome of the decision will have a very significant impact on the application of law across all EU member states in the area of child maintenance, particularly for states who have recently joined and who intend to join the EU in future."
Granted anonymity and referred to as TKF, the man had been ordered to pay £83.55 a month until his son finishes full-time education.
That decision was made by a Polish court five years before the country's accession to the EU in 2004.
Divorced from his wife, TKF has lived in Northern Ireland since 2006.
He issued judicial review proceedings against the Clerk of Petty Sessions for the District of Belfast and Newtownabbey after the maintenance decisions were registered and declared enforceable in Northern Ireland in 2013.
The man claimed that he knew nothing about the 1999 Polish court proceedings, neither attending not being represented at any hearing.
His lawyers claim the enforcement decisions were unlawful because they relate to maintenance orders made when Poland was not an EU member state.
Mr McGarrity also emphasised the wider significance of the case.
With a hearing due before the end of the year, he predicted: "It could well be one of the last cases from the United Kingdom to be heard in the European Court - so the eyes of the legal world will be fixed on the outcome."