Mayor Zohran Mamdani issued Gov. Kathy Hochul a stunning ultimatum Tuesday while unveiling his $127 billion budget proposal – tax the rich or he’ll raise property taxes by nearly 10%.

The eye-popping preliminary spending plan for the 2027 fiscal year would increase the city’s budget by a whopping $11 billion from 2026, and contains few cuts.

But the Democratic socialist brazenly claimed he would be “forced” to hit the pocketbooks of everyday New Yorkers if Hochul and Albany don’t comply with his push to raise income taxes on the wealthy.

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He cast the 9.5% property tax increase — which would affect about 3 million residential units and 100,000 commercial properties — characterizing it as a regrettable “last resort” to close the city’s estimated $5.4 billion budget gap.

“I do not want to raise property taxes,” Mamdani said while presenting his budget proposal.

“When faced with this crisis, the question is who should pay these taxes? I believe that it should be the wealthiest New Yorkers, the most profitable corporations. I believe that they can afford to pay a little bit more,” he said.

It was a clear message to Hochul, whose approval Mamdani needs to make his long-promised “rich tax” a reality – but who has voiced staunch opposition to the idea as she faces re-election in the fall.

Without that approval, Mamdani warned he would be “forced to go down a second, more harmful path of property taxes,” which would be “placing the onus for resolving this crisis on the backs of working and middle-class New Yorkers.”

The staggering property tax proposal would only generate about $3.7 billion, city officials said. 

Mamdani also proposed raiding more than $3.25 billion from the city’s main reserves and millions of dollars more from other savings accounts, to close the fiscal gap.

But even while Mamdani has been framing that deficit as a crisis – which Hochul pitched in $1.5 billion to help cover just this week — his new proposal made few sizable cutbacks, leaving many skeptical about his bullish charge at Albany.

“The mayor should ensure that every one of the people’s $127 billion is used well, before asking them to dig into their pockets,” said Citizens Budget Commission executive director Andrew Rein.

“The best choice is to eliminate spending that does not improve New Yorkers’ lives and make government more efficient and effective,” he said.

City Comptroller Mark Levine warned that Mamdani’s property tax proposal would have “dire consequences,” and that the city was currently “under the greatest fiscal strain since the Great Recession.”

“Our property tax system is profoundly unfair and inconsistent, and an across-the-board increase in this tax would be regressive,” said Levine.

He wasn’t the only city Democrat frustrated with their new socialist comrade commandant – with sources telling The Post that even “the most progressive members of the [City] Council are annoyed.”

“They all know Hochul isn’t going to raise taxes. Even progressives are saying what the hell is this. This whole thing is a mirage,” one source said. 

“This is one of the most outrageous, fiscally irresponsible things. This has real world impact. He is causing panic,” the source said.

The City Council would have to approve the increase to property taxes, the only taxes the mayor can control without the OK of the state Legislature.

Mamdani’s plan includes some frightening prospects: a nearly 22% tax for residential homes and townhouses or buildings with just three or fewer units, more than 13.6% for larger apartment buildings and a nearly 12% tax for commercial properties like storefronts or office buildings.

If it passes, the owner of a single-family home in Park Slope with a market value of around $3.2 million, and assessed by the city at $44,000, would pay around $9,500 in yearly property taxes, up from roughly $8,700 currently.

A condominium unit on the Upper West Side currently assessed at $120,000, would go from paying $14,926 to $16,345 in annual property tax.

Property taxes haven’t been raised since just after the Sept. 11, 2001 terror attacks.

Mamdani’s budget proposal – a 9.6% increase over fiscal year 2026’s $115.9 billion – includes:

The proposal is just the first step in a months-long process, which will include negotiating changes with the City Council. The finalized budget is due by June 5 and would go into effect July 1.

“At a time when New Yorkers are already grappling with an affordability crisis, dipping into rainy day reserves and proposing significant property tax increases should not be on the table whatsoever,” City Council Speaker Julie Menin wrote in a statement.

Albany’s budget is due by April 1, though the state has been known to push weeks past that deadline.

There has long been support among state legislators for tax hikes similar to Mamdani’s proposed 2% increase for those earning more than $1 million, but Hochul has routinely been opposed. 

She also told reporters Tuesday she was “not supportive” of his property tax idea.

“I’m not supportive of a property tax increase, I don’t know that that’s necessary,” she said during an unrelated event.

Some experts believed there was little chance of Mamdani’s 9.5% property tax proposal going anywhere, predicting that the state would likely step in with even more funding to bail the city out.

“It’s a strategy. It’s posturing — for now,” political consultant Geroge Arzt said. “It’s the usual game between the mayor and the legislature. Mamdani is playing the same game every other mayor has played at this point in the budget process.”

One Democratic insider put it more bluntly.

“It really is stunningly risky,” they said.

“Broad-based property tax increases are historically so deeply unpopular that he is essentially betting his political career on a game of chicken with Albany.”

— Additional reporting by Haley Brown, Matthew Fischetti and Hannah Fierick