In a conference room in Manhattan on Wednesday night, Mayor Eric Adams and Daniel S. Loeb, the hedge fund manager, met with other business leaders and political brokers to discuss how to stop the rise of Zohran Mamdani and possibly bolster Mr. Adams’s re-election campaign.

The business leaders were impressed that Mr. Adams was already staging a public fight against Mr. Mamdani, several people familiar with the meeting said. Earlier in the day, during an interview on “Fox & Friends,” Mr. Adams called Mr. Mamdani a “snake-oil salesman.”

Mr. Mamdani, a democratic socialist state assemblyman from Queens, on Tuesday shocked the New York political establishment by outperforming Andrew M. Cuomo, the former New York governor, in the Democratic primary for mayor. Mr. Cuomo is now considering whether to run as an independent in the general election, or end his campaign altogether.

Should Mr. Cuomo withdraw, Mr. Mamdani is poised to face off against Mr. Adams, who is running as an independent; Curtis Sliwa, the Republican founder of the Guardian Angels; and Jim Walden, a lawyer also running as an independent.

The prospect of Mr. Mamdani’s campaigning as the Democratic standard-bearer in a city where Democrats outnumber Republicans by six to one has sent shivers down the spines of many New York business leaders, who recoil at his plans for expansive new government programs funded with tax increases on corporations and the wealthiest New Yorkers. Some have quickly begun to throw their support behind the incumbent mayor, despite the scandals that have tarnished his tenure.

Andrew Epstein, a spokesman for Mr. Mamdani, said the businessmen at the meeting were simply scared of “our plan to tax them a little bit more to fund an agenda to lower the cost of living and improve the quality of life for all New Yorkers.”