I am a hard core coke fan myself, but this is unbelievably stupid.
The union claims it was because of his union work:
… but they may be biased in that assertion. 
Yeah right. He wasn’t fired for drinking Pepsi, there is more to it than that. Makes for a good story though!
Who would drink that vile concoction anyway. ~blech~
I avoid Pepsi at all costs. If I go to a restaurant where they only have Pepsi products, I’ll get a Dr. Pepper.
Anyway, like Samarm said, I’m SURE it was due to something else.
~J
What about that commercial where the Coke driver and the Pepsi driver each swap drinks?
Yet another reason not to drink soft drinks.
Ignoring the union issue for the moment, this isn’t so silly as a matter of policy as one might think. Suppose someone had a camera and snapped a photo of the truck driver, in his Coke uniform, sipping a Pepsi? And suppose the photo started making the email rounds? It would be awful PR for Coca-Cola. It would basically be free advertising for Pepsi. Coca-Cola treats this kind of thing seriously for a good reason – why hand your chief competitor an advertising coup?
Dewey Cheatem Undhow, likethis?
In all seriousness, the odds that the worker simply got sick of Coke after a while is not inconceivable. When I worked at Domino’s, my manager didn’t eat pizza. He said that after two years of working delivering, making and being around pizzas, he got sick of 'em. He could still eat wings, but he never ate pizza. Maybe the same is true with this guy … he got tired of Coke and drank a Pepsi. I don’t recall anyone getting all bent out of shape when various people would order from KFC or whatever. They didn’t order from rival pizza companies because they worked in pizza and didn’t want any. If they did, the stuff was right there to make it with.
The way I see it; if he was tired of drinking Coke, there’s plenty of other drinks that the Coca-Cola company makes that he could’ve/should’ve drank.
Here’s another news story that might give a different point of view. And a better one, IMHO.
This particular story says he was caught drinking Diet Pepsi.
Woof! That could be the answer. No sense of taste. 
Maybe he was tired of drinking Coke all the time. That I can understand.
But…
(italics mine)
Sheesh.
When I worked for Coke as a member of the promotions team we were told flat out that not only could we only drink Coke products while at work, we also could only eat at restaurants that served Coke products.
We were told if caught drinking other product, we would be let go.
Any Coke product was fine though, including Powerade and bottled water (Dasani I think?).
You mean when you went out to lunch? Or any time?
That’s pretty ridiculous! And you couldn’t bring a bottle of juice or something, or a carton of milk if you wanted to?
He did say while they were at work, so I’m guessing as long as they weren’t in work hours they could eat and drink what they want.
I temped at Dr Pepper a few years ago, and the very first instruction we were given by Dr Pepper was that we were allowed to drink only Dr Pepper products while we were on the premises. I had to not only finish my daily morning diet Coke before I entered the parking lot, but I had to dispose of the bottle, too. “On the premises” meant even while I was in my car. Furthermore, if we brought back a fast food cup from lunch with any other soft drink company logo on it, we had to transfer it to another cup or wrap a napkin around it to hide the other logo.
This made complete sense to me. No matter where your workstation was, there was a good chance that a non-employee could catch sight of you, and how would it look for a Dr Pepper employee to be swigging a diet Coke?
Gaspode: the picture isn’t loading for me for some reason.
Somehow I feel as though I should weigh in on this topic. 
It’s a shame the dude got fired, but a Coke delivery man drinking a Pepsi on his rounds is kinda like a Fed Ex delivery dude wearing all brown, if ya get my drift.
Dewey, it’s a picture of a guy in a Pepsi truck drinking a bottle of Coke.
lorinada-what about plain water in a drinking bottle?
This is really weird.