Dogs can negatively affect the wellbeing of people and nature, but if this changes along a socioeconomic gradient, then social inequity might be at fault. Here, we identify environmental injustice at the city scale by modeling differences in the density of urban dog populations according to varying levels of socioeconomic development across municipalities of Chile's capital, Santiago. Our analysis demonstrates a strong relation between dog density and social inequity, specifically because dog density increases along with poverty, but decreases in municipalities with higher municipal income. We offer specific proposals to ameliorate and reverse this inequity. These results expose another aspect of the impacts people and nature are subjected to by dogs, adding a new social lens to address the dog problem worldwide.