The Massachusetts senator has been one of the most outspoken figures against the banking industry since the 2008 financial crisis, and donors tell Politico that if Warren is the pick for vice president, it could really hurt Clinton’s donations. The presidential candidate is hoping to raise $1.5 billion for her campaign. So far she has raised $289 million, and she’s relying on Wall Street for more.

One Democratic donor said putting Warren on the ticket could drive Clinton’s entire Wall Street base away. Sheila Krumholz, executive director of the Center for Responsive Politics, says that could be a huge problem for her. “Things are so volatile now with all of the outside groups that all it can take is pissing off one billionaire on Wall Street to make it difficult,” she told Politico. “And you don’t run national campaigns for as many years as Clinton has without some serious support from Wall Street.”

But after Bernie Sanders’ campaign, Clinton is feeling pressured from the left. Considering Warren for the No. 2 spot jibes with Sanders’ call to break up the big banks, and many are hoping to see her on the ticket, including Senate Minority Leader Harry Reid. However, if Warren is the VP, the Clinton administration’s relationship with the private sector could be strained from day one, which Wall Street donors say would be disastrous for the economy.

Clinton’s campaign says they’re “not at the point of ruling anyone in or out.” The candidate said earlier this month that Warren is “eminently qualified for any role,” and she “[looks] forward to working with her.” Stephanie Taylor, co-founder of the Progressive Change Campaign Committee, added that whether or not she’s the vice presidential pick, “it’s hard to imagine Hillary Clinton not wanting a very large role for Elizabeth Warren at the table.”

Numerous Wall Street donors identified Virginia Senator Tim Kaine as their preferred vice presidential nominee.

Hillary Clinton’s campaign and Elizabeth Warren could not immediately be reached for comment.