you really have no clue on how a union can affect a business. I guess that's why industries are so flourishing in US now.
There are good unions and bad unions. But even non-union wages aren't low enough to keep manufacturing from going abroad, where people will work for a few dollars a day (which is not enough for anyone to bother with in the US). Manufacturing is going abroad with or without unions.
As for Smike's comment, the low dollar has been good for exports and has helped the economy from being worse than it otherwise might be. But I've heard at least one economist say that no nation has ever exported itself out of a recession; I'd suspect it's just not a big enough part of the economy.
Anyway, there are far more issues in this election than Obama's position on unions. Unless one is a one-issue anti-union voter, in which case go ahead and vote against him.