Political procedures aimed at solving conflicts are becoming popular in agri-environmental economics. They are considered as substitutes for market trans­ac­tions. Ecological lobbying groups put pressure on poli­ticians to enforce ecological main structures, while farmers oppose them. Undefined property rights pose problems and statutory regulations are discussed. The paper applies a political economy model of social bargaining to the provision of an ecological main structure. It shows how a tragedy of the commons problem may prevail. Then it outlines a social optimum of field margin provision. Finally, it provides a solution to the establishment of socially acceptable rules in a political economy framework. Also, a payment scheme is introduced.