Big Wall Street banks are so upset with U.S. Democratic Senator Elizabeth Warren's call for them to be broken up that some have discussed withholding campaign donations to Senate Democrats in symbolic protest. Representatives from Citigroup, JPMorgan, Goldman Sachs and Bank of America, have met to discuss ways to urge Democrats, including Warren and Ohio Senator Sherrod Brown, to soften their party's tone toward Wall Street. Citigroup has decided to withhold donations for now to the Democratic Senatorial Campaign Committee over concerns that Senate Democrats could give Warren and lawmakers who share her views more power, sources inside the bank told Reuters. The Massachusetts senator's economic populism and take-no-prisoners approach has won her a strong following. Warren, a former Harvard Law professor who joined the Senate Banking Committee after taking office in 2013, has accused big banks and other financial firms of unfair dealings that harm the middle class and help the rich grow richer. In a Dec. 12 speech, she mentioned Citi several times as an example of a bank that had grown too large, saying it should have been broken apart by the Dodd-Frank financial reform law. In January, Warren angered Wall Street when she successfully blocked the nomination of a banker Antonio Weiss to a top post at the Treasury Department. She argued that as a regulator he would likely be too deferential to his former Wall Street colleagues.