As a growing number of vacant storefronts dot the city, Mayor Bill de Blasio [last week] said he wants to penalize landlords who leave the shopfronts sitting empty," report Rich Calder, Elizabeth Rosner, and Ruth Brown.

Mayor de Blasio made the comments during an interview on The Brian Lehrer Show on WNYC.

The idea is still highly speculative, but from Mayor de Blasio's comments on the show, two salient details of his proposal emerged: that the tax would apply to storefronts and that the legislation could get "done through Albany," a reference to the State Legislature.

As for the problem the vacancy tax would tackle, "[a] number of recent studies have found retail corridors in prosperous Manhattan neighborhoods are struggling with double-digit vacancy rates, from 27 percent on Amsterdam Avenue on the Upper West Side to 20 percent on a stretch of Broadway in Soho. Five percent or less is generally considered 'healthy.'"