If you can smack a tax on their imports, why not already do it? This only works if you are a union/trading-block/superpower with the leverage to do so - and as the world gets globally competitive morally punishing taxes will require more and more "fighting the invisible hand" i.e working against the interests of free trade.

To re-iterate the point that probably got my original post downvoted: It helps to have a large military-industrial complex to enforce embargos.