This paper explores how agency was used within a police-hospital collaboration to implement a planned change designed to increase the sustainability of a cross-sector collaboration. A longitudinal, qualitative case study involving pre-and-post interviews with 20 police officers and 20 healthcare workers allowed us to capture multiple perspectives of the planned change over time. Analysis of case study data reveals three major findings: (1) organizations with limited power can have agency in cross-sector collaborations when they are perceived to have legitimacy and urgency; (2) the extent to which the implementation of a planned change influences perceptions of agency depends on the organizational context of the perceiver; and (3) different levels of analysis (i.e., meso versus micro) support different conclusions with respect to the role of agency in the sustainability transition process. More broadly, our study highlights the role of perception when investigating agency within sustainability transitions.