SPOKANE, Wash. -

Burger King's deal to merge with Canada's Tim Hortons fast food chain has a lot of people talking, especially about the potential tax benefits for the King. 

Burger King is set to become the third largest fast food company in the world, with more than 18,000 restaurants world wide. 

Sales for Burger King have been flat over the last couple of years, so a merger with another fast food giant makes business sense.

But what's creating a lot of anger among American citizens is something called tax inversion. It's why many think Burger King is merging in the first place. So, what is tax inversion?

Essentially it's when an American company purchases another company overseas. Then they effectively move their company headquarters to that new overseas location, and that means their earnings are taxed at a far lower rate in that country. 

America currently has the highest corporate tax rate in the world at just over 39%.

Tax inversion is completely legal, but it doesn't sit well with many Americans. 

Now, many are taking to the internet to call for a boycott of Burger King, even Ohio Senator Sherrod Brown asking people not to eat at the fast food chain. 

Burger King, however, has said the merger is not about saving money on taxes. 

Experts say the company will be saving about $5 billion to $10 billion a year. 

But this isn't just about Burger King. The U.S. has seen a large increase in companies moving headquarters overseas to save money on taxes. By some estimates, that could cost the U.S. $19 billion over the next ten years.