The Board of Supervisors on Tuesday night voted to move ahead with an initial draft of a just-cause ordinance—albeit one that would exclude most of West Marin, after county staff added an exemption for properties that contain fewer than three rental units. The exemption would constrict the ordinance’s applicability in unincorporated Marin as a whole by nearly 70 percent. 

The ordinance, which would sunset in two years, requires landlords to give both tenants and the…