It's an article titled "The Moral Status of the Corporation," from the Journal of Business Ethics, from Volume 10, Issue 10, copyright 1991, by R.E. Ewin. (Use ProQuest or a university library to access the entire article--that is, unless you're liberal with your cash and want to pay $30 for the privilege.)
The conclusion gets to the heart of the matter:
Because they are artificial and not "natural" people, corporations lack the emotional make-up necessary to the possession of virtues and vices. Their moral responsibility is exhausted by their legal personality. Corporations can have rights and duties; they can exercise the rights through their agents, and they can in the same way fulfill their duties. If necessary, they can be forced to fulfil [sic] their duties. The moral personality of a corporation would be at best a Kantian sort of moral personality, one restricted to the issues of requirement, rights, and duties. It could not be the richer moral life of virtues and vices that is lived by the shareholders, the executives, the shop-floor workers, the unemployed, and "natural" people in general."There are two ways this could run. For an affirmative running Kantian morality, the argument shows that corporations must be held to the same standards--"requirement, rights, and duties." For the negative running virtue ethics (or, perhaps, some other non-Kantian moral framework), it lines up well with an argument that corporations cannot be held to the same standards of approval or disapproval of various virtues and vices.
As a tangent, one must question the "natural / artificial" dichotomy that grounds Ewin's argument. Would an enhanced human, with artificial limbs, neurological prosthetics (such as a computer chip that would aid in memory) or other "artificial" characteristics be considered a "natural" person? Why wouldn't a robot programmed to obey Asimov's three laws be morally culpable for breaking them?