"It will not work," Warren said in a statement emailed to The Huffington Post.
Warren has been a vocal advocate for reining in big banks that she says wield too much power in Washington after their recklessness triggered the 2008 financial meltdown.
Citigroup, JPMorgan Chase, Goldman Sachs and Bank of America have discussed ways to soften Warren's strong tone, Reuters reports, and representatives of some have raised the idea of cutting campaign donations to Democrats. Only Citigroup -- a frequent target of Warren's criticism -- so far is publicly withholding money from the Democratic Senatorial Campaign Committee.
Cutting donations, Warren said, won't end her demands.
"They want a showy way to tell Democrats across the country to be scared of speaking out, to be timid about standing up, and to stay away from fighting for what’s right," Warren wrote. "... I’m not going to stop talking about the unprecedented grasp that Citigroup has on our government’s economic policymaking apparatus ... And I’m not going to pretend the work of financial reform is done, when the so-called 'too big to fail' banks are even bigger now than they were in 2008."