New York City Mayor Zohran Mamdani speaks about the fiscal year 2027 budget in New York City on May 12, 2026. (Photo by TIMOTHY A. CLARY / AFP via Getty Images)

Timothy A. Clary | Afp | Getty Images

From New York to Vancouver to London, a once-niche policy idea is moving into the mainstream of urban finance: taxing pied-à-terre properties , second homes, vacation apartments, and luxury units that sit partially or entirely unused.

New York City is just the latest example, with Mayor Zohran Mamdani and New York State Governor Kathy Hochul supporting the tax as part of a state and city effort to make up a big budget hole .…