In this paper, we study the effect of trade secret protection and product characteristics on the organization of supplier relations, namely on the exclusivity of contracts between automobile manufacturers (OEMs) and auto part suppliers. When an OEM transfers sensitive technology necessary to customize a procured component, it faces the risk of misappropriation of the blueprint, particularly in an environment with weak intellectual property rights. As the supplier may use the knowledge acquired to serve other rival firms, an OEM can decide to use an exclusivity clause on the supplier's side to protect its trade secrets. The analysis employs a unique dataset including 11 years of contracts between automotive parts suppliers and manufacturers worldwide obtained from the Marklines ``Who Supplies Whom'' platform. In an environment with strong intellectual property protection, an OEM is less concerned about its technology being exposed to competitors as it can sign a non-disclosure agreement with its supplier that is enforceable under high-quality legal institutions. This allows the supplier to safely engage in business with and provide inputs to other manufacturers while the protection of the OEM's trade secrets is guaranteed. In a country where the OEM cannot rely on legal enforcement, instead, the only means of protecting its sensitive information is by imposing exclusivity to limit the involvement of its supplier with competing OEMs and prevent the exploitation of its trade secrets. We find a robust positive association between the strength of trade secrets protection in a country and the number of OEMs that a supplier from that country works with. Mapping an index of relationship specificity for each auto part to the component definition provided by Marklines, the effect of trade secrets protection is especially strong for products characterized by an intermediate level of relationship specificity susceptible to the threat of expropriation.