Scanning CAC at the chowhall

Unit is saying if we go to the chowhall instead of eating these MREs we are going to get charged. As far as I know, they scan for numbers purposes to see how much food they need to order/prepare. Is that apart of any kind of database? Can they actually figure out who was there? I have not, but what would stop you from even going to during the week if happened to be on base?