Sens. Jeff Flake, R-Ariz., and Chris Coons, D-Del., called on President Trump Monday to back off the Federal Reserve.

“We are concerned about your recent comments harshly criticizing the Federal Reserve (Fed) for its interest rate decisions,” the bipartisan duo wrote Trump in a letter sent Monday. “If you undermine the Fed’s credibility, you are putting the U.S. economy at risk.”

Trump’s criticism of the Fed as “overly aggressive” in raising interest rates has met a chorus of senators on both sides of the aisle telling him to stop bashing the central bank — or at least reiterating the importance of an independent central bank. Trump has tied a recent dip in stock prices to the Fed’s plans, sketched out by his appointees to the Fed’s leadership, to raise short-term interest rates closer to pre-financial crisis levels.

Flake and Coons went a step further than past critics, adding that they believe the president does not have grounds to remove Fed Chairman Jerome Powell for disagreement over what the Fed's target interest rate should be.

“Never in the 105-year history of the Fed has a chair been removed by the President,” the two wrote Trump. “In fact, the law prohibits a President from removing a Fed board member, except for cause. Disagreement over interest rates clearly is not justifiable cause.”

Though the pair of senators warned Trump that attempting to exert political influence over the Fed could wreck the economy, drawing comparisons with Zimbabwe, it’s unclear how much leverage they themselves have to stop Trump should he try to remove Powell. Neither sits on the Senate Banking Committee, which has jurisdiction over the Fed, and Flake will retire from the Senate at the end of this Congress. The Arizona Republican, a frequent critic of the president, has suggested that Trump should be challenged in the 2020 Republican presidential primary campaign.