The Federal Reserve Act of 1913 gave the Federal Reserve authority to set monetary policy in the United States.

http://en.wikipedia.org/wiki/Federal_Reserve_System#cite_note-91

Monetary policy

Further information: Monetary policy of the United States

The term "monetary policy" refers to the actions undertaken by a central bank, such as the Federal Reserve, to influence the availability and cost of money and credit to help promote national economic goals. What happens to money and credit affects interest rates (the cost of credit) and the performance of an economy. The Federal Reserve Act of 1913 gave the Federal Reserve authority to set monetary policy in the United States.