Last week, the left-wing mayor faced backlash after touting sweeping property taxes by 9.5 percent - a move that would hit millions of homeowners - despite promising only to make the rich pay more.

Mamdani swept into office in January after a commanding win in November's election on the back of pledges to take on the city's richest residents. A key campaign pledge was a flat 2 percent tax on individuals earning over $1 million.

But less than two months into his term, the 34-year-old has admitted it might not be as simple as he thought. On Tuesday he warned he may need to hike property tax rates in NYC by 9.5 percent to raise money. 

Real estate insiders warn the proposal is a numbers-defying misstep that could push rents higher and speed up the exodus of taxpayers to lower-tax states such as Florida and Texas. 

'Even the discussion of a 9.5 percent hike is enough to influence buyer behavior and cause irritations in the market,' Douglas Elliman's Ben Jacobs told Fox News Digital. 

'Some buyers have considered Nassau, Westchester, Long Island, and even Florida or Texas as alternatives because they just don't agree with [NYC] politics.'

He continued: 'Higher corporate and wealth taxes can trigger a chain reaction. Reduced investment and relocation of high earners shrink the city's tax base, which often indirectly affects middle-class households. Even if they aren't the direct target, over time these economic ripples can influence affordability, property values and access to services.' 

Michelle Griffith of Douglas Elliman told the outlet: 'The mention of a 9.5 percent hike can pause decision-making, especially for those weighing options in the suburbs or out-of-state markets. We're already seeing clients seriously evaluate alternatives in Nassau, Westchester and beyond, factoring taxes heavily into affordability calculations.'

She continued: 'Ultimately, buyers want predictability. When policy proposals create uncertainty, whether on taxes, rent or regulations, it directly impacts the market. People are not just looking at the sticker price of a property.'

'Stability and transparency in tax and assessment policies are key to keeping NYC's middle-class families confident in making big housing decisions.'

Mamdani said the tax is a 'last resort' if the state's governor, Kathy Hochul, refuses to sign off on the his plan to raise income taxes on the wealthy. 

In other words, if he cannot hammer the rich with higher income taxes, he is prepared to turn to the one lever he directly controls - property taxes. 

That would not just hit penthouse owners in Manhattan. The property tax hike would hit three million single-family homes, co-ops, and condos as well as over 100,000 commercial buildings, Mamdani said.