How is it possible for a state to make something illegal in another jusidiction?

I've been hearing about this Georgia law that would make it illegal for women (presumably residents of Georgia) to have abortion procedures in other states. Just how the hell does that work?

It would be like punishing people who go to Europe and have a drink before they are 21. Or punishing people who go to Amsterdam and smoke hemp. It's not illegal there - so if I'm doing it there, how does the state have a right to punish me for doing something _legal_.

Is this just plainly an illegal law on its face, or am I missing something?