Answer:
The Federal Reserve is in charge of the monetary policy in the United States. It expands or reduces the money supply (the total amount of money in the economy) by raising or lowering the interest rate.
There is a relationship, in the short run, between unemployment and money supply. The higher the money supply, the lower the unemployment rate, and viceversa: the lower the money supply, the higher the unemployment rate.
This relationship exists because when the money supply increases, the interest rate falls, if the interest rate falls, investing becomes cheaper, and as a result, firms invest more and hire more workers.
The opposite happens when the money supply is contracted: interest rates rise, investing becomes more expensive, and firms hire less people.
This is why the Fed has a great deal of power when it comes to employment in the economy.