But Farrokh Hormozi, a Pace University economist with the public administration department, said such talk is hyperbolic. "This is New York City," Hormozi said. "I don't think the market will react or people will leave because of a 2 percent tax hike. The dynamism of New York City is worth far more than that."
Others agree that a democratic mayor won't trigger a Wall Street rebellion. "I don't think there's going to be much revolt," said David Mark, editor in chief of Politix and author of "Going Dirty: The Art of Negative Campaigning."
Mark added with de Blasio's comfortable lead and apparent lock on the Democratic base, he's recently had time to reassure financial elites that he doesn't have it in for them. He called Wall Street the "hometown industry" of New York before a gathering of moguls and financiers earlier this month, The New York Times reported.
But others disagree, including billionaire Wilbur Ross. He worries Mayor Bloomberg's hard-won gains against crime and urban decay could be lost, according to the Times.
Jack Hidary, a tech entrepreneur who is running for mayor as an independent and is polling in the single digits, warned in his own campaigning that he has heard "a lot of people telling us they're considering moving their main residency somewhere else," in light of a potential de Blasio win.
"I fear that capital will take flight and talented people will take flight," Hidary said.
But Hormozi of Pace University is again skeptical of such claims. "They give the Republican mayors of the last two decades too much credit. The transformation of New York City from the '70s to the '80s was mostly nourished by economic conditions," he said.
Hormozi said he doesn't think a Mayor de Blasio would have much impact on Wall Street one way or another. "But there's a feeling of nervousness," he said.
Neither the de Blasio campaign nor that of his Republican opponent Lhota responded to inquiries for this story.
—By CNBC's Matt Twomey. Follow him on Twitter