Mayor de Blasio (photo: Edwin J. Torres/ Mayor's Office)

A report released by the city Independent Budget Office has raised questions about the potential effects of the so-called “mansion tax,” a proposed part of Mayor Bill de Blasio’s affordable housing strategy that would levy a 2.5 percent surcharge on the sale price over a threshold of $2 million for residential properties.

De Blasio put forward a version of the mansion tax proposal, which requires approval by the State Legislature and Governor Andrew Cuomo, in mid-2015. It failed