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.