In the world of compliance, you may sometimes wonder if that code of ethics really works. Lisa L. Shu, Francesca Gino, and Max H. Bazerman presented their research that a code of ethics really can reduce bad behavior: Dishonest Deed, Clear Conscience: Self-Preservation through Moral Disengagement and Motivated Forgetting.
Their studies provided evidence that morality and memory function as sliding scales and are not fixed dimensions of a person. They found that once people behave dishonestly, they disengage, setting off a downward spiral of future bad behavior and increasingly lenient moral codes. They also found that this slippery downward slope can be counteracted with ethical codes, that increase awareness of ethical standards.
If a situation permits dishonesty, then you should expect dishonesty. At the same time, merely reminding employees about established ethical codes, could counteract the effect of a permissible situation.