In the aftermath of the outbreak of the Severe Acute Respiratory Syndrome in 2003, the Housing Department launched a marking scheme with an aim to improving the environmental hygiene in public housing estates in Hong Kong. The marking scheme operates like a penalty-point system. Public housing tenants who have received sixteen points are evicted by the Hong Kong Housing Authority (HKHA) and then barred from applying for public rental housing for two years. In this sense, the marking scheme imposes both tenure conditionality and access conditionality on tenants. Although the scheme can potentially arrest anti-social behaviour and other misconducts in public housing estates, the choice of public housing tenants as the sole target of control has not been clearly explained. This question is closely related to the origins of the marking scheme.This paper attempts to explain its origins from three different perspectives-public health, welfare conditionality and policy opportunism. Apparently, the first two theses cannot fully justify the scheme. Alternatively, the substance of the marking scheme seems to match the ideology of policy opportunism quite well as the scheme appears to be an initiative of the HKHA to strengthen its sovereignty over public housing resources in the city.