There have been repeated calls for more ecological approaches to Sustainable HCI, and for the inclusion of the sociopolitical, structural, historical, and geographical aspects that shape technology-mediated practices of sustainability. Contributing to this discourse, and drawing from scholarship on Law and IT, this paper explores how the law, technology design, market mechanisms, and social norms enable and constrain behaviours — that is, how they regulate them. We use these modalities to discuss two digital technologies: a gig-work platform mediating practices of waste transportation, and an eco-visualisation platform scraping sustainability reports of publicly listed companies. The analysis expands on the set of dynamics that characterise the relations between these practices of sustainability, technology design, and regulation. We conclude by discussing the relevance of this conceptualisation for HCI, specifically in defining the roles of designers as regulators, and regarding design for sustainability as constituted through varying entanglements of these modalities.