U.S. President Donald Trump on Monday said he was firing Federal Reserve Gov. Lisa Cook over alleged improprieties in obtaining mortgage loans, an unprecedented step that could test the boundaries of presidential power over the independent monetary policy body should it be challenged in court.

Trump said in a letter to Cook, the first African-American woman to serve on the Federal Reserve's governing body, that he had "sufficient cause to remove you from your position” because in 2021 Cook indicated on documents for separate mortgage loans on properties in Michigan and Georgia that both were a primary residence where she intended to live.

Cook responded several hours later in a statement emailed to reporters through the law office of lawyer Abbe Lowell, saying of Trump that "no causes exist under the law, and he has no authority" to remove her from the job she was appointed to by former U.S. President Joe Biden in 2022. "I will continue to carry out my duties to help the American economy."