A Polish court has ruled some parts of European Union treaties are incompatible with the Polish constitution.
Challenging a pillar of European integration, and sharply escalating a dispute between Brussels and Warsaw.
Poland's Law and Justice party government is embroiled in a battle of values with Brussels, over issues such as the judicial independence, media freedom and LGBT rights.
The party says it has no plans for a so-called "Polexit", but critics say that by challenging the supremacy of EU law over national law, the government jeopardizes Poland's long-term future in the bloc, and even the stability of the European Union itself.
Pro-EU protesters shouted "shame" and "traitor" at the deputy foreign minister on Thursday (October 7) night, after the verdict was announced.
The constitution won, Pawel Jablonski told reporters.
Poland's prime minister welcomed the ruling on Facebook on Friday (October 8). It was Mateusz Morawiecki who'd requested Poland's Constitutional Tribunal to rule on whether EU law takes precedent over the Polish constitution.
The European Commission said it was "concerned", and emphasised that the primacy of EU law was at the core of the union.
Anger from EU members came thick and fast, with France's European affairs minister, Clement Beaune, calling it an attack on the Union, and Luxembourg saying Poland was "playing with fire".