Abstract Health and welfare organizations are encouraged to collaborate in regional, cross-domain networks. Although the literature has shown that policy changes can influence the effectiveness of existing networks, the impact of the Dutch Integral Care Agreement ( Integraal ZorgAkkoord, IZA) is not yet known. We investigated this in a longitudinal qualitative case study of a network that has been in existence for a long time. The results show that after implementation of the IZA, a new overarching network at the healthcare administrative regional level was established. This led to uncertainty regarding the objective, composition, and sustainability of the existing network. A division emerged in the existing network between members who participated in the new network and those who did not. Organizations that participated in the new network questioned their participation in the existing network, to reduce administrative pressure. Organizations that only participated in the existing network doubted their participation because they lost sight of the network’s purpose and experienced a lack of transparency regarding decisions made in the new network. The Dutch national government and policymakers would do well to seek close alignment with practice when further developing the IZA.