Five UK nationals are going to court in the Netherlands in a campaign to keep their EU citizenship after Brexit.
They want a Dutch judge to press the European Court of Justice (ECJ) to clarify their rights.
The ECJ, if it decides to make a ruling, could guarantee such rights as freedom of movement after the UK leaves the European Union.
An ECJ decision would affect all British nationals living in the European Union.
The European court could rule that all member states must guarantee the rights of Brits in the respective states where they reside - under European law.
About 85,000 British nationals live in the Netherlands.
The interim deal thrashed out between the UK and Brussels in December does outline some of the rights British citizens in Europe will keep after Brexit, such as the ability to live and work on the continent.
But some vital questions, like free movement, still swirl around.
'We've been forgotten'
Some of the group of five say they have been disheartened by the confusion and speculation about what their life will be like after Brexit.
"Just because the UK voted to leave, it shouldn't be able to force citizens to give up their rights," says Stephen Huyton, one of the Brits taking the court action on Wednesday.
The Netherlands does not currently allow foreigners to have dual nationality, in most cases.