When my co-workers and I go to lunch, we frequently attend fast-food restaurants and mall food courts. When placing the food order, some people (some Catholic, some not) order the food as a carry-out even though they fully intend to eat inside the restaurant. This is done to avoid paying the sales tax. Some of the people are just “cheap,” while others feel that they pay enough taxes as it is. Most of them feel that this is harmless and many other people do it, so it’s no big deal. Would this be a sin? If so, how serious?
Deliberately choosing to avoid paying legitimate expenses is a form of dishonesty and stealing, petty though the expense might be. Given that we likely are talking about a small amount of money, the sin likely would be venial, but that does not justify petty dishonesty and theft. Although it may seem to your co-workers that this does no harm and is no big deal, one of the things such petty dishonesty/theft does is lower someone’s inhibitions against more serious acts of dishonesty and theft. And, as you’ve already noticed, another thing it can do is spread the problem: Note, for example, that one of your co-workers’ justifications for their action is that “many other people do it.”