Éire / Ireland

Ok there's a few things that need to be more clear in this discussion before one should answer:

1. Ireland is not part of the EU
2. Taking US officials hostage because the US jails their own citizen is very different than some sort of exchange negotiation
3. The US is still "somewhat" working together with other countries to not just jail tourists for being "immigrants"

With all these things in mind, I don't see why the EU should be doing any punishing. And even if Ireland or the UK wants to do something, it's debatable whether she should be protected under the laws of Ireland and the UK.

If the EU is going to do any punishing to protect everybody from the US, it will be in the form of requests and demands, after which it will be sanctions. Look at the sanctions against Russia if you want to know how that looks.