The European Court of Justice (ECJ) has been asked to consider whether Britons living in the 27 other member states can retain their rights as EU citizens after Brexit.
The Dutch courts have referred the case, which could have implications for a million Britons living in other EU countries, to the ECJ.
Campaigners have suggested that the case could also protect the EU citizenship of UK residents born before Brexit.
The judge in Amsterdam said in a written ruling that “there has to be more clarity about the consequences of Brexit for EU citizenship”.
UK citizens who live in the Netherlands went to the court in a bid to retain their EU citizenship rights after Britain leaves the bloc in March 2019.
Lawyers for the Dutch state dismissed their case as legal fiction.
Leading barrister Jolyon Maugham QC, who supported the Netherlands case, said the decision of the ECJ – also known as the Court of Justice of the EU (CJEU) – could even have implications for British nationals in the UK.
“The case – if determined by the CJEU in our favour – could lead not only to the retention of EU citizenship for UK residents living in the EU,” he said.
“It could lead to all born before Brexit – even if living here in the UK – retaining the boon of EU citizenship.”
The issues referred to the ECJ are whether Brexit automatically leads to the loss of the EU citizenship and its associated rights and, if it does not, whether conditions or restrictions should be imposed on those rights.