UPC Code

I have a question about the UPC code printed on the container of our supplements. I was going through another supplement company’s website (John Davies, Mike Mahler, Kelly Baggett knows these guys) looking at their protein and amino acid products. They were offering half price on them but only if you put in the UPC code of a competitor’s product you’ve bought. Why would they ask for that and what type of information are you giving away?