• Background Smoke-free housing policies in multiunit housing are increasingly widespread interventions to reduce smoking and secondhand smoke exposure. Little research has identified factors that impede compliance with smoke-free housing policies in low-income multiunit housing and test corresponding solutions. • Methods We are using an experimental design to test two compliance support interventions: (A) a “compliance through reduction (via relocation and reduction in personal smoking) and cessation” intervention targets households with smokers and involves support to shift smoking practices to designated areas, reduce personal smoking, and deliver in-residence smoking cessation support services via trained peer educators and (B) a “compliance through resident endorsement” intervention involving voluntary adoption of smoke-free living environments through personal pledges, visible door markers and/or via social media. We will compare randomly sampled participants in buildings that receive A or B or A plus B to the NYCHA standard approach, • Discussion This RCT addresses key gaps in knowledge and capitalizes on key scientific opportunities by: 1) leveraging the federal mandate to ban smoking in a public housing system of more than sufficient size to conduct an adequately powered RCT; 2) expanding our understanding of smoke-free policy compliance beyond policy implementation by testing two novel treatments: a) in-residence smoking cessation and b) resident endorsement, while 3) addressing population and location-specific tobacco-related disparities. At the conclusion of the study, this RCT will have leveraged a monumental policy shift affecting nearly half a million NYC public housing residents, many of whom disproportionately experience chronic illness and are more likely to smoke and be exposed to secondhand smoke than other city residents. This first-ever RCT will test the effects of much-needed compliance strategies on resident smoking behavior and secondhand smoke exposure in multiunit housing. Trial registration: Clinical Trials Registered, NCT05016505 Registered: August 23, 2021 https://clinicaltrials.gov/ct2/show/NCT05016505