Written employment contracts may improve the conditions of agricultural workers in developing countries, but farmers as employers often prefer less formal oral arrangements. We evaluate whether farmers' preferences, which are deeply rooted in traditional norms, can be influenced through a group awareness campaign. In a randomised experiment in Côte d'Ivoire, we show that such a campaign increases farmers' preferences for written contracts and for contract features involving social benefits for workers. The campaign also increases farmers' likelihood to initiate concrete steps towards signing a contract with their workers. We conclude that group-based interventions can change farmers' traditional views about employment relations.