Donald Trump’s claim that he had a “fiduciary duty” to minimize his taxes has sparked a conversation about business ethics. Individuals like Trump have no legal duty to keep as much money as possible. To whom would they even owe such a duty? But for publicly traded companies, the story is a bit different. Federal and state laws assign corporate leaders a rather vague responsibility to take care of the best interests of the company and its shareholders, which some courts have interpreted as a requirement that companies prioritize earning money for shareholders above all else.

In any case, what really matters is what people who run companies believe they’re obligated to do. And, as the Bentley University professor Jacob M. Rose found in a study published in 2007, corporate directors take what they see as a legal duty to maximize profits very seriously. Rose’s experiment involved posing ethical questions to 34 active directors of U.S. Fortune 200 corporations. He divided them into two groups, asking 17 of them to address the issues from the perspective of a director of a publicly held company—essentially as they would in real life. The other 17 were told to imagine themselves as partners in a privately held partnership, a role in which there are no public shareholders for management to be responsible to.

Rose asked them to evaluate two scenarios involving legal loopholes that a company might take advantage of. One asked about cutting down “one of the last remaining stands of old-growth forest in Oregon,” the other about the release of a carcinogenic toxin into the environment. In both cases, doing the environmentally destructive thing promised to reward the company financially. The directors’ responses varied dramatically depending on whether they thought of themselves as corporate directors or company partners. Only one of the “directors” declined to cut down the forest, compared with seven of the “partners.” And just two “directors” chose not to emit carcinogenic toxins, while 14 of the “partners” did.

Asked about their reasons for their decisions, almost all the directors mentioned their primary responsibility to their shareholders. In a typical response, one director wrote that “I cannot violate my responsibilities to owners because I have personal feelings about the decision.” In contrast, the subjects who were acting as partners made it clear that they were weighing their personal wealth and the success of their business against the guilt they would feel about socially destructive behavior. The study results offer some powerful evidence that, at least from the perspective of corporate directors, the duty to maximize shareholder earnings easily overwhelms other concerns.