The group of four MSPs and MEPs will ask the Court of Session to rule on whether Article 50, the mechanism set out in EU treaties that was used to trigger Brexit, can be reversed.
The UK Government insists Article 50 is irreversible, but UK Supreme Court judges did not make a definitive ruling on the matter when deciding earlier this year whether MPs had to give their approval before the provision in the Treaty of Lisbon could be triggered.
The group, made up of Green MSPs Andy Wightman and Ross Greer, SNP MEP Alyn Smith and Labour MEP David Martin, argue that Article 50 can be reversed if EU member states unanimously agree, and will ask Scottish judges to refer the issue to the European Court of Justice in Luxembourg for confirmation.
They have written to Brexit Secretary David Davis and the Advocate General for Scotland, Lord Keen, asking them to respond by 12 December or face a legal challenge.
A crowdfunding appeal was launched last night seeking £50,000 to pay for the action.
In a statement, the group said: “We know it is possible to stay in the EU, if the other member states give us permission.
But the destiny of the United Kingdom should rest in the hands of our Parliament. It must be our elected MPs who decide what road to take.
The statement goes on “Many experts believe we can choose to stay in the EU without permission. That, if we want, we can just withdraw our notice.
“But there is only one way to be sure: a court has to decide what Article 50 means. And because Article 50 must mean the same thing to everyone, a national court can’t give the answer.
“Only the specialist European Court in Luxembourg can interpret Article 50 definitively. So we will ask the Court of Session in Scotland to ‘refer’ it to Luxembourg.
“This is the only way to give our Parliament the best negotiating hand. To maximise its power if the right choice is to stick with what we have.”
Conservative MSP Oliver Mundell called the legal challenge a “complete distraction” by the “loony left”, and his Tory colleague, the Aberdeen South MP Ross Thomson, said: “Lets be absolutely clear that UK voted in a democratic and open referendum to leave the EU.”
“That result should be respected and delivered on and the UK Got will work to ensure best Brexit deal for Scotland.”