Interesting idea. The similarities to embargo are obvious, but I think it's sufficiently distinct. Some thoughts:
I feel like the reveal/choose mechanic needs to go. Not because it's too political or anything, but because it weakens the card too much. If you can only block action cards your opponent already has, there's a good chance he wasn't planning to buy more, anyway. You should just be able to pick a pile to block. It's probably wise to restrict it to action (or maybe kingdom) cards, though, because a) putting one of these on the provinces would be really obnoxious, let alone two or three, and b) it helps keep the feel distinct from embargo. I'll assume you can move a zombie to any action card supply pile for the rest of my comments.
With the +$2, I'm a little worried that this card is too close to a strictly-better duchess. The fact that you can gain duchesses for free is probably enough to compensate, though.
The blocking effect could be much stronger in multiplayer, because often nobody would want unblock a pile for fear of giving their opponents an advantage.
This card should swing the balance toward big money, since the money player will probably have the actions he needs before you can block them.
This card counters itself pretty strongly, because you aren't impeded by the zombies on the turn you play it. The only alternative counter is to buy the zombie on top of the pile you want to get at, so either way, you end up with a zombie in your deck. Generally, I don't like that sort of thing. I'd like there to be an alternate way to get rid of the zombie. Paying extra $ to get the card might work, but isn't very thematic. Maybe discard an action card to lure away the zombie?
