Elizabeth Warren has a clear message for Wall Street: "Bring it on."

The senator from Massachusetts said Monday that she will continue to call for financial reforms and for big Wall Street banks to be broken up, despite potential retaliation against Democratic candidates.

Last week, Reuters reported that some banks, including Citigroup (C) and J.P. Morgan (JPM), might withhold campaign contributions to Senate Democrats because of Warren's negative portrayal of Wall Street.

According to Reuters, Goldman Sachs (GS) and Bank of America (BAC) also participated in a meeting to discuss the anti-bank rhetoric, although the idea of withholding donations wasn't talked about. Goldman has already made its donation for the year.

"You bet I believe it's a serious threat," Warren told a packed room at a Barnes & Noble in New York City's Union Square -- a few miles north of Wall Street.

"It is so brazen. If they think they can say in public, 'I don't like your tone, I don't like the way you talk about financial regulation' ... I got news for them: bring it on," the Democrat said.

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Warren stressed that she only wants two things from Wall Street: banks shouldn't be able to cheat people, and no financial institution should be able to risk destroying the economy because it's too big to fail.

"If they want to fight on either one of those, I'm ready," she said to much applause.

Warren says no to presidential run: Several members of the audience held up "Elizabeth Warren for President" signs and chanted "Run, Liz, Run" during the event.

"No, I am not running for president," Warren said. "I am not going to run for president."

Instead, she called herself a "nerd" who loves her Senate job. Her top priorities at the moment are reducing the interest rate on student loans, increasing funding for the National Institutes of Health and raising the federal minimum wage above $7.25 an hour.

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Emiljana Ulaj was one of the people holding a sign at the bookstore and urging Warren to run. An immigrant from Albania, she has a full-time job but believes the American Dream is at risk.

"I hope she's just deliberating about running and didn't chose this moment to announce," Ulaj, 28, told CNNMoney. She was pleased to hear Warren stand up to the banks, "That's when you know you're making change."

What's ahead: The stakes for Warren may be higher if Sen. Charles Schumer, a Democrat from New York with close ties to business, becomes the Senate Democratic leader after Sen. Harry Reid retires in 2016. Schumer is widely viewed as the top candidate for the leadership post.

Schumer and Warren would likely clash on financial regulation, and he might push her to soften her tone in order to help fundraising. If the banks didn't contribute, the Democratic Senatorial Campaign Committee could lose up to $15,000 per bank a year -- and possibly more if individual bankers stopped donating as well. Warren is already trying to fight back by asking supporters for donations in a blog post Friday.

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Warren is currently promoting her book, "A Fighting Chance." She read from a passage about her fight against the big banks to create the Consumer Financial Protection Bureau, which she says has forced banks to return $5 billion "to consumers they cheated."

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Correction: An earlier version of this story incorrectly said that Goldman Sachs might withhold its campaign contribution to Senate Democrats, citing reporting from Reuters.