U.S. President Donald Trump risks hurting investor sentiment if he removes Jerome Powell as chair of the Federal Reserve, according to a former Fed governor.

“To fire a Federal Reserve governor or chairman would be a very unprecedented move, it would result in turmoil in the financial markets, it would be something that you really don’t want to do because you don’t need an absolute increase in uncertainty which this would bring about,” Robert Heller, a member of the Fed’s Board of Governors from 1986 to 1989, told.

Heller’s comment came as Bloomberg, citing people familiar with the matter, reported on Wednesday that Trump said he believes he has the authority to demote Powell.