At first, I assumed this was yet another case of a simple incident being misunderstood and reaching urban "ain't PC awful" legend status, given that I could only find reference to it in WorldNutDaily and assorted rightwing blogs, but
this article appears legit.
Even with the article in a real news source, I'm still a bit amazed that a corporation would actually fire anyone in a dispute over their political beliefs. Officially, he was fired for insubordination, so I'm assuming that things got nasty when he was asked to take his signs off his vehicle, but I'm still having a hard time picturing things reaching that point, based on my experiences with various corporate HR departments. At any rate, while I personally think it's asinine that he would even be asked to remove the signs in the first place, it's Cargill's right to fire who they please. Perhaps Mr. Padilla might take a moment to consider the irony in his having lost his job due to discrimination against his political view that discrimination based on sexual orientation is fine.