This article strives to find out how monetary contestation, when brought before the courts, can generate institutional change. The goal is to show if the contestation conveyed by local currencies at a specific point can be considered as a driving force via the evolution of monetary rules. This article focuses on the case of eusko—a French local currency of Basque Country. What has become the most extended French and currently European local currency was the subject to a legal conflict between the State, through the prefecture of the Pyrénées-Atlantiques, and the City of Bayonne. By using a qualitative approach by a set of semi-structured interviews, the article analyzes, helped by the theoretical framework of John R. Commons, how the dissemination of new monetary practices could be selected by judicial and political powers, respectively. Based on empirical results, and considering the Commonsian concepts of “artificial selection” and “institutionalized compromise,” I conclude that the legislation changed due to this legal conflict. This change has paved the way for other French municipalities to mobilize the terms of the agreement and aim to pay part of their public expenditure in local currency.