But what exactly are negative interest rates and how do they work?
Central banks have one key goal in mind when they cut rates: encourage people and businesses to spend their money.
That's why the Fed slashed interest rates to a historic low -- almost 0% -- in the midst of the financial crisis in 2008.
When people aren't earning any interest in the bank, they look around for other ways to make money.
Implementing a negative rate is an even bigger shock to jumpstart spending.
Janet Yellen: Negative rates possible in U.S. - Feb. 11, 2016