(CNN) — The Government Accountability Office says the Trump administration broke the law when it withheld US security aid to Ukraine last year that had been appropriated by Congress — an issue at the center of the impeachment of President Donald Trump. In a decision issued Thursday, the GAO said that the White House budget office violated the Impoundment Control Act, which says that funds appropriated by Congress cannot be withheld by the White House. “Faithful execution of the law does not permit the President to substitute his own policy priorities for those that Congress has enacted into law. OMB withheld funds for a policy reason, which is not permitted under the Impoundment Control Act (ICA). The withholding was not a programmatic delay. Therefore, we conclude that OMB violated the ICA,” the GAO said. A hold was placed on the Ukraine aid at the beginning of July 2019, and the agencies were notified at a July 18 meeting that it had been frozen at the direction of the President, a week before a phone call between President Donald Trump and Ukrainian President Volodymyr Zelensky which later became the reason an impeachment inquiry was launched into the President.