The universal law of nature formulation ('Act as though the maxim of your action were to become by your will a universal law of nature') is a more substantial and controversial claim

Thus, Kant argues, a rational will, insofar as it is rational, is a will conforming itself to those laws valid for any rational will. Addressed to imperfectly rational wills, such as our own, this becomes an imperative: “Conform your action to a universal non-natural law.” Kant assumed that there was some connection between this formal requirement and the formulation of the CI which enjoins us to “Act as though the maxim of your action were to become by your will a universal law of nature.” But,