I have mixed feelings about the US not letting countries who opposed the war bid for contracts.
But it is US tax dollars, so they have a right not to take bids from people they don't want to take bids from.
How would you like it, say, if you had to buy groceries from a firm you didn't like? And where being forced to?
Its US cash, they can spend it how they see fit. Of course there is a political side to this too, and some countries may get really pissed off with the decision.