The company has to deliver a roadmap to address the issues by January, they said. In a statement, Citigroup said it was "completely committed" to addressing the shortcoming found in its 2021 resolution plan. "As part of the transformation Citi has embarked upon, we are making significant investments in our data integrity and data management, as the letter notes," the bank said. "We will leverage that work to remediate the shortcoming identified today, as we acknowledge there is much more work to do." Shares of Citigroup slipped 2.2% in early trading. With CNBC's Jeff Cox.