This article focuses on the migration policy crisis in France to illustrate how social movements contribute to the epistemic construction of ‘crises’ of European Integration. To tackle politicization, we compare the framing and mobilization choices by grassroots actors in solidarity with asylum-seekers and groups aiming to defend national borders from them. Using original Protest Event data and 21 face-to-face interviews, we find that the construction of the crisis as a policy failure crucially reshaped mobilization on both sides of the conflict. Specifically, direct social actions allowed the two camps to respond to a context perceived as critical, politicizing the crisis in light of the declining trust in representative institutions, while also responding to the growing demand for efficacy and concreteness. The findings offer novel empirical insight on movement–countermovement interactions and contribute to the scholarly debate on the relation between crises and the politicisation of contentious issues in Europe.