The person making this argument thinks their argument is watertight because of its structure, and will likely not listen to any suggestion that natural laws are not a component of the laws described in the first premise.

If people think the structure is watertight and that the is argument valid because of that, maybe pointing out the structural flaw in clear terms would get through to them. Specifically, this one's called a fallacy of four terms, though it's in disguise; the word law is used to mean human-designed law in the major premise and any kind of law in the minor premise. The fact that the word also occurs in the phrase natural laws adds to the fun, too.

If going into even deeper detail might help, linguistics has a name for this sort of phenomenon: autohyponymy. It's when a word has a kind of "default general sense" in addition to one or more specific meanings, which occasionally leads to mix-ups. In this case, we have the hypernonym law (=all kinds of laws) and its hyponym law (=piece of human legislation). Another set of examples of the concept of autohyponymy would be the hyperonym dog (=dog of either gender) and its hyponyms dog (=male dog) and bitch (=female dog).