In Fortune

“The primary purpose of the law is to fill empty homes,” supervisor Dean Preston, the law’s chief backer, told Fortune Friday. “Holding housing off the market for a long time, when there are people who need housing, is bad for our city,” he said. “Our hope is that [the tax] is enough to change the decision making of the real-estate speculator or the owner of the property.”

Sometimes, developers have a strategy of buying buildings, removing longtime tenants, and then reselling at a profit, Preston said. More recently, some new constructions have failed to sell units amid a market slump, creating “zombie buildings,” the San Francisco Chronicle reported last month.