Trust has traditionally been regarded as conducive to ethical decision making. However, empirical studies on the relationship between trust and ethical decision making are rare, especially those concerning the negative effects of trust. Therefore, our study aimed to provide empirical evidence in this area. An experiment was designed to investigate whether trusted parties are more likely than non-trusted parties to enter into a collusion that will have unfair consequences for a third party. The results showed that trusted parties are significantly (...) more likely to collude than are non-trusted parties. Furthermore, an ancillary analysis revealed the mechanism of trust. First, participants with a stronger need to collude were the most likely to collude in the trust group. Second, experimental and hypothetical settings generated different results, and we suspect that real harm plays a vital role. Overall, we conclude that the absence of trust serves as an impediment to collusion. (shrink)