Gabrysch, who started in August, wrote that the CFO's statements about city finances are relied upon by investors, rating agencies, the City Council and taxpayers, and "must be complete and accurate." She said she was "not able to fulfill those obligations under the conditions in which I have been asked to serve."

"It has become apparent, however, that to continue in this role would be to compromise my integrity and professional obligations," she wrote. "I therefore have concluded that I must step down from my role, and hereby tender my resignation."

The mayor's office accepted the resignation effective immediately and pushed back sharply, saying Gabrysch was largely absent during critical budget preparations and had directed the city treasurer to issue a $75 million payment without proper legal authority. A mayoral spokesperson said Gabrysch acted before Nov. 2 legislation had taken effect, violating established procedures.

Gabrysch dismissed the administration's response as an "effort to deflect from the serious issues at stake and attack those who attempt to hold them accountable," calling it "disappointing but not surprising."

The resignation is the third CFO departure from Johnson's administration in less than a year, a turnover rate that drew immediate criticism from aldermen.

"Mayor Johnson was on his third CFO in less than a year. The 3rd just resigned after a few weeks on the job. This was after she pointed out the serious flaws in the Johnson budget on the first day of hearings," Ald. Scott Waguespack wrote on social media.

Ald. Bill Conway, vice chair of the Finance Committee, called for "an immediate and robust investigation," arguing that Gabrysch's letter suggests she was asked to present false information. He warned that the controversy could harm Chicago's credit rating and fiscal standing.

"If Mayor Johnson asked his CFO to act or speak dishonestly, that is a shocking act against taxpayers and potentially criminal fraud," Conway said.

The mayor's office said it will refer the matter to the city's Office of Inspector General for independent review, adding that it welcomes a full review of the conduct at issue.

Comptroller Michael Belsky, who helped recruit Gabrysch, said he was disappointed by the news but defended the administration's transparency. "As is sometimes the case in any workplace, certain professional relationships and working arrangements do not work out," he said. "Any suggestion to the contrary is simply incorrect."

Belsky will serve as acting CFO effective immediately.

The upheaval comes as Chicago faces a serious budget crisis, with the administration pointing to decades of mismanagement. The resignation letter's allegations and the administration's counterclaims have thrust the city's financial management into the spotlight just as budget deadlines approach, raising questions about the integrity of the city's financial statements and the stability of its leadership.