We propose and test a new channel for the transmission of monetary policy. We show that when the Fed funds rate increases, banks widen the interest spreads they charge on deposits, and deposits flow out of the banking system. We present a model in which imperfect competition among banks gives rise to these relationships. An increase in the nominal interest rate increases banks' effective market power, inducing them to increase deposit spreads. Households respond by substituting away from deposits into less liquid but higher-yielding assets. Using branch-level data on all U.S. banks, we show that following an increase in the Fed funds rate, deposit spreads increase by more, and deposit supply falls by more, in areas with less deposit competition. We control for changes in banks' lending opportunities by comparing branches of the same bank. We control for changes in macroeconomic conditions by showing that deposit spreads widen immediately after a rate change, even if it is fully expected. Our results imply that monetary policy has a significant impact on how the financial system is funded, on the quantity of safe and liquid assets it produces, and on its lending to the real economy.
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