The King County Council on Tuesday adopted an ordinance prohibiting algorithmic rent‑fixing in unincorporated King County, extending a policy other cities have adopted to limit the use of third‑party platforms that recommend or coordinate rents across multiple landlords.

Council Member Teresa Mosqueda, the item’s sponsor in committee, described the ordinance as a preventive step to stop large corporate landlords from using data‑driven platforms to collude on prices. “We don’t want there to be any technological tool that basically replaces what would otherwise be dark smoky backrooms where collusion would be happening,” Mosqueda said in committee.

The ordinance, adopted as proposed substitute 2025‑0267 with council amendments, draws on language from comparable municipal laws and federal antitrust standards and contains a narrow exemption clarifying the chapter does not apply to short‑term rentals. The council also added a requirement that county websites and tenant‑protection communications include plain‑language information about the new law so renters can understand their rights.

Council members noted the measure targets platform‑driven collusion by large managers and aggregated data services, not ordinary landlord pricing decisions by single small owners. The ordinance passed on a 9–0 roll call.

The council asked county staff and communications teams to update public materials explaining the new rule; enforcement mechanisms will be implemented consistent with county code and in alignment with federal law.