(CNN) Elizabeth Warren is so fed up with one of the country's top Wall Street regulators that she's fired off a lengthy letter expressing her "disappointment."
A 13-page letter, to be exact.
The Massachusetts Democrat, one of the most vocal and influential Wall Street critics in Washington, on Tuesday sent a blistering note to Mary Jo White, the head of the Securities and Exchange Commission, requesting that she "step up."
"I voted for your nomination despite my concerns about your lack of experience as a regulator," Warren wrote. "I am disappointed by the significant gap between the promises you made during and shortly after your confirmation and your performance as SEC Chair."
Warren has long called on the SEC to take tougher enforcement actions and raised various concerns about White's work, but Tuesday's letter is one of the most striking condemnations yet of White's tenure as head of the regulatory agency.
The senator highlighted numerous problems with the way that the SEC is run, including the agency's failure to extract admissions of guilt from financial institutions in legal settlements. Warren also took issue with White's recusals from numerous enforcement investigations due to potential conflicts of interest presented in part by her husband's clients.
Those recusals, Warren said, have hindered the SEC's ability to move forward with prosecution.
According to Warren's letter, she and White met in person last month -- a meeting that clearly did little to reassure the senator.
"You said little that indicated that you would be changing your practices at the SEC," Warren said.
White fired back at Warren's criticism on Tuesday, saying in a statement that she is "very proud" of the SEC's achievements under her watch and accusing the senator of "mischaracterization."
"I am very proud of the agency's achievements under my leadership, including our record year in enforcement and the Commission's efforts in advancing more than 30 congressionally mandated rulemakings and other transformative policy initiatives to protect investors and strengthen our markets," White said. "Senator Warren's mischaracterization of my statements and the agency's accomplishments is unfortunate, but it will not detract from the work we have done, and will continue to do, on behalf of investors."