A prominent Democratic U.S. senator called on a top regulator on Wednesday to impose growth restrictions on Citigroup as the Wall Street bank struggles to fix ongoing regulatory problems. In a letter to Acting Comptroller of the Currency Michael Hsu,

The Massachusetts Democrat called on a top government regulator to restrict the growth of the nation’s fourth-largest bank.

In a letter to Acting Comptroller Michael Hsu, Democratic Sen. Elizabeth Warren urged the regulator to curtail the megabank's growth in response to its failure to improve its risk management programs.

ET: Updates with statement from Sen. Warren and stock movement. Sen. Elizabeth Warren (D-MA), who has been a long-time critic of Wall Street banks, asked one of Citigroup's (NYSE:C) regulators to limit the company's growth as it deals with numerous regulatory problems.