Federal Reserve Board Governor Lisa Cook on Thursday sued President Donald Trump to block his unprecedented attempt to fire her, setting off a legal battle likely to end up at the Supreme Court.

The suit, filed in federal court in Washington, D.C., also names Fed Chairman Jerome Powell and the Board of Governors itself as defendants.

Trump said Monday that he was removing Cook because of allegations that she committed mortgage fraud in connection with two residential properties she owns.

“This case challenges President Trump’s unprecedented and illegal attempt to remove Governor Cook from her position which, if allowed to occur, would the first of its kind in the Board’s history,” Cook’s attorney, Abbe Lowell, wrote in the lawsuit.

“It would subvert the Federal Reserve Act ... which explicitly requires a showing of ‘cause’ for a Governor’s removal, which an unsubstantiated allegation about private mortgage applications submitted by Governor Cook prior to her Senate confirmation is not,” Lowell wrote.