The National Bank.
Andrew Jackson had long despised the Bank because he felt the Bank was a monopoly and unconstitutional which was why he decided to veto the Bank which essentially threw the United States into the Panic of 1837. He had removed all federal funds from the Bank and deposited them in various state banks (also known as pet banks) which is where the controversy comes in.
People felt that Jackson’s decision to destroy the Bank and remove all funds from it was an abuse of executive power and that he was disregarding the Constitution during his Bank War, which is why Jackson is sometimes known as King Andrew Jackson.