Mayor Zohran Mamdani is officially pressing the City Council to drain the Big Apple’s rainy day fund — setting up a showdown with Speaker Julie Menin, The Post has learned.

The Mamdani administration this week formally requested that the council amend the city’s current spending plan to allow siphoning $980 million from a savings fund created under Mayor Bill de Blasio in 2021.

The fund currently has $2 billion, and city officials have never tapped into it — even during the COVID pandemic and the migrant crisis.

But Mamdani, who has proposed a record $127 billion spending plan, contends the city’s rainy day has arrived — in the form of a projected $5.4 billion budget deficit.

The near-billion-dollar ask starts a 30-day clock for council members to vote on the measure, which is unlikely to success given Menin and other lawmakers have already spoke out against pulling from the city’s savings.

“The responsible path forward is not to deplete our financial safety net, but to pursue real efficiencies and sustainable solutions,” Menin said last week.

“The council will continue pushing for the long-term savings and fiscal discipline needed to protect New York City’s financial stability.”

The high-stakes disagreement partly hinges on what can realistically be done to shore up New York City’s finances.

Menin argued that the city could make about $1.7 billion in spending cuts – largely coming from eliminating long-unfilled jobs from the budget – for the 2027 fiscal year instead of tapping reserves.

But Mamdani’s team has pushed back, countering that Menin’s savings math doesn’t add up.

The budget standoff comes as Mamdani plans to poach Menin’s budget chief, Richard Lee, to become his Finance Department commissioner, sources confirmed.

The top concern for the lawmakers has been a downgrade of the Big Apple’s bond rating, which would increase borrowing costs and significantly hurt city finances.

Last week, two top bond rating companies warned of a downgrade if city savings were depleted.

“The main thing we were concerned about is how it would affect the bond rating. Now we are seeing that in real time,” said Council Finance Chair Linda Lee.

“To be clear, we are not cutting services,” she added. “There is money to be found and savings to be found. We shouldn’t go into the rainy day fund.”

City Hall officials didn’t respond to a request for comment Tuesday, but Mamdani said last week that he was “committed to working with the council” to address the deficit.

“However, the savings plan that was put forward frankly raises more questions than it answers,” he said.

The prospect of tapping reserves is also opposed by many budget watchdogs.

“We think the rainy day reserves should be protected to protect New Yorkers during a recession. We have a real budget problem but this is not the time to take from the rainy day reserve,” Citizens Budget Commission president Andrew Rein said.

“We think there is significant savings in the city where we can close this budget gap if were shrinking programs that aren’t helping New Yorkers’ lives.”