Here is a list of the top donors for the 2008 election-
http://www.opensecrets.org/bigpicture/topcontribs.php?cycle=2008
Your argument is a non-sequitur- Regardless of where any unions might place on the Fortune 500 list, what matters is how much money they donate, and who they donate it to.
Note that there are unions at slots 8,20,26,29,30,32,38,41,42,44,45,and 51. That's at least 12 different unions among the top 51 donors.
And note who the top donors (business or unions) give money to- predominately the Democrats- 23 of the top 50 are listed as strongly or solidly Democratic, while only 1 of the top 50 donors is listed as either solidly or strongly Republican.
45 of the top 100 are Democratic, while only 4 are Republican.
Again, I am fine with any restrictions placed on donations. But lets apply them equally, and it should include union donations, too.
LAST ELECTION! You can't judge on ONE ELECTION, Obama winning was a forgone conclusion. The Bush administration doomed any Republican no matter who they were. If you are a company, who would you donate to if you know who is going to to win? The losing side, so you alienate those in charge for the next four years? Anyone who couldn't bring themselves to donate to the Dem's just didn't donate. Come on. This is PoliSci 101.
EDIT:
In an up in the air election, it is a very different story:
http://www.opensecrets.org/bigpicture/topcontribs.php?cycle=2002&Bkdn=DemRep