Lefty Gen-Z City Councilman Chi Osse is preparing to challenge Democratic House Minority Leader Hakeem Jeffries in the US House next year — against the explicit objections of mayor-elect Zohran Mamdani, The Post has learned.

“He said he wants to strike when the iron is hot,” one insider said of the TikTok pol.

The source said that Mamdani had told Osse that he didn’t want him to challenge Jeffries in the primary, believing it would disrupt the fragile peace between the far-left of the party and moderates.

Mamdani worked for months to woo the establishment of the party to unite ahead of his mayoralship.

“Strike while the iron is hot?” another insider complained, adding, “How about listen to the next mayor, who is the hottest thing in politics right now.”

The second source confirmed Osse has already started hiring his staff to challenge the Brooklyn Democrat.

The falling-out between Osse and Mamdani — two social-media-savvy pols — even kept Osse from attending the victory party follow the mayor-elect’s historic win last Tuesday night.

The Post got mixed reports as to whether Osse was a card-carrying member of the Democratic Socialists of America (DSA), or just a far-left party member.

The feud highlights what insiders have opined will be a real problem for the 34-year-old mayor-elect as he tries to enact his lofty socialist policies.

Insiders say Mamdani needs to keep the peace between the party establishment, including Gov. Kathy Hochul, and the insurgent far-left — which is trying to capitalize on his win and challenge more moderate.

Osse’s announcement is expected to come this week.

Osse referred The Post to his spokesperson, who did not immediately return calls

A rep for Jeffries did not immediately respond Sunday.

Osse referred The Post to his spokesperson, who did not immediately return calls

Osse had been an outspoken backer of Mamdani.

Jeffries had endorsed Mamdani late last month, just before early voting in the mayoral race began.

It came after he dragged his feet for months, in an apparent struggle over the now mayor-elect’s far-left agenda and hostility toward Israel.

“Zohran Mamdani has relentlessly focused on addressing the affordability crisis and explicitly committed to being a mayor for all New Yorkers, including those who do not support his candidacy,” Jeffries declared in his endorsement last month.

“In that spirit, I support him and the entire citywide Democratic ticket in the general election.”

Since arriving in Congress in 2013, Jeffries had glided through every reelection bid in his deep blue Brooklyn district — which includes Clinton Hill, Bed-Stuy, Brownsville, Canarsie and then extends west to include Sheepshead Bay and Seagate.

But, during the second Trump administration, the Brooklyn Democrat has come under intense pressure from the progressive left to put up more of a fight.