Although grassroots initiatives in the renewable energy transition are flourishing, their embeddedness in local contexts challenges their capacity to spread their impact on a broader scale. Certainly, while scaling up has been described as difficult to combine with local embeddedness, little is known on the specific nature of the tensions involved in combining the two. Studying a federation of citizen renewable energy (RE) cooperatives in the south of France, we show that the engagement in a scaling-up process at a regional level generates three main kinds of tensions associated with specific dimensions of local embeddedness: natural, cultural, and political. We emphasize how these dimensions are likely to be threatened when the federation engages the cooperatives in a rapid scaling-up dynamic in which the drive to industrialize projects and find funding is dominant. We acknowledge the effects of these tensions on grassroots sustainability initiatives and collective organizing processes.