Downstream firms increasingly recognize the importance of integrating social and environmental concerns with their businesses. As a consequence, they urge to create incentives for their suppliers to invest in corporate social responsibility (CSR) activities. Contracts to provide these incentives are rarely observed in practice. If not totally absent, contracts may be incomplete, in that unforeseen contingencies or some CSR attributes that are difficult to measure may not be included in the contract. We show that incentives for CSR investments can also be provided through the supply chain structure, which consists of the distribution of ownership rights over the firms' assets of production, and involves horizontal and/or vertical alliances among supply chain members. Motivated by examples in agricultural contexts, this study adopts the property rights approach to study the impact of supply chain structures on the adoption of CSR activities. We show that the structure that best incentivizes CSR investments depends on the interaction between CSR vertical synergy, free‐riding, and countervailing power. One of the main findings is that the alliance between suppliers is beneficial only if the revenues generated by a downstream investment are sufficiently high. In fact, only in this case, the suppliers can appropriate a sufficiently large stake of the revenues generated downstream, thanks to their countervailing power. When the upstream investment costs become high, however, the suppliers will invest in CSR only if the downstream distributor is vertically integrated. The resulting structure of a cooperative will best incentivize CSR investments only if the CSR vertical synergy between the two tiers of the supply chain is sufficiently high.