President Donald Trump said Monday night that he’s firing Federal Reserve Governor Lisa Cook, an unprecedented move that would constitute a sharp escalation in his battle to exert greater control over what has long been considered an institution independent from day-to-day politics.

Trump said in a letter posted on his Truth Social platform that he is removing Cook effective immediately because of allegations that she committed mortgage fraud.

Cook said Monday night that she would not step down. “President Trump purported to fire me ‘for cause’ when no cause exists under the law, and he has no authority to do so,” she said in an emailed statement. “I will not resign.”

Bill Pulte, a Trump appointee to the agency that regulates mortgage giants Fannie Mae and Freddie Mac, made the accusations last week. Pulte alleged that Cook had claimed two primary residences -- in Ann Arbor, Michigan, and Atlanta -- in 2021 to get better mortgage terms. Mortgage rates are often higher on second homes or those purchased to rent.

Trump’s move is likely to touch off an extensive legal battle that will probably go to the Supreme Court and could disrupt financial markets. Stock futures declined slightly late Monday, as did the dollar against other major currencies.