the eu has exclusive competence over trade/custom policy, monetary policy, justice (the ecj is the highest jurisdiction in the eu), immigration, health, agriculture, etc. anything the eu pokes its nose in, member states must follow. national law ranks lower than eu law. the problem is that, unlike national law, people can't vote for eu law. they can vote for eu deputies, but the eu parliament doesn't have any power. the people who actually decide eu law are unelected. it's a legal oligarchy.
Belgium