> is there some kind of "commerce clause" type loophole for this
The EU is not just a commercial organization. It is an actual political union. The English-speaking press tends to hate mentioning this, but it is the truth. The treaty of Lisbon says that the goal of the European Union is to create an "ever closer" union between the member states. Every member state signed up for this.
> I would've thought that this was outside the scope of the EU
Few things are outside the scope of the EU.
> was power constitutionally transferred to the EU parliament at some point?
It is a very complex topic, but the short answer is "yes". Member states agree to translate EU parliament decisions into national law at their own time. They have the ability to veto any initiative through other channels.
> If a member nation refused to obey an EU law (or whatever it is), what sort of punishment or sanction could be applied to them?
This things are usually dealt with through diplomacy. There is a lot of tolerance. Often nothing happens but many types of sanctions (usually economical) are possible.
The US is also (obviously) a political union, but the Feds cannot legislate on every issue, some issues are left to the states. One exception is on matters where interstate commerce is affected, where the Feds have broad power. That's the commerce clause exception GP was referring to.
If you want further detail, look up Wickard v. Filburn. An activity taking place within one individual's property in a single state can be regulated under the interstate commerce clause, so long as a case is made that it affects interstate commerce. Sounds wild, and it is, but the dependency graph is such that we can't change that now without upsetting the whole cart.
Even wilder: the other day I ran across https://en.wikipedia.org/wiki/Gonzales_v._Raich which apparently held that growing marijuana, for personal use under state law, is also interstate commerce. Is there anything at all that isn't interstate commerce?
I mean, that's basically Wickard v. Filburn 60 years later and with a different plant. It actually seems downright reasonable if you accept Wickard as settled law, which it is.
The EU is not just a commercial organization. It is an actual political union. The English-speaking press tends to hate mentioning this, but it is the truth. The treaty of Lisbon says that the goal of the European Union is to create an "ever closer" union between the member states. Every member state signed up for this.
> I would've thought that this was outside the scope of the EU
Few things are outside the scope of the EU.
> was power constitutionally transferred to the EU parliament at some point?
It is a very complex topic, but the short answer is "yes". Member states agree to translate EU parliament decisions into national law at their own time. They have the ability to veto any initiative through other channels.
> If a member nation refused to obey an EU law (or whatever it is), what sort of punishment or sanction could be applied to them?
This things are usually dealt with through diplomacy. There is a lot of tolerance. Often nothing happens but many types of sanctions (usually economical) are possible.