SAN FRANCISCO (AP) – Airbnb says it is stepping up efforts against hosts who violate San Francisco’s laws on short-term rentals.

Airbnb executive Chris Lehane tells the San Francisco Chronicle that the vacation-rental website will now investigate hosts who list multiple homes (http://bit.ly/1or5VhA). Starting Saturday, Airbnb also will purge hosts who have turned private homes into illegal hotels.

Airbnb’s pledge comes after years of complaints that conversions of homes into short-term rentals for out-of-towners are worsening housing shortages.

Current law in San Francisco says homeowners can list only their own residences for vacation rentals. However, Airbnb tells the Chronicle that 1,149 of its house listings in San Francisco are controlled by people with more than one home on the site. That’s one-fifth of all Airbnb home listings in the city.