You can get fired for drinking Pepsi or Coca-Cola

A Coca-Cola employee can get fired if caught drinking Pepsi, like wise a Pepsi employee can get fired if caught drinking Coca-Cola.

Yes you would be fired. Upon being hired /employed you will actually sign an agreement stating you will not purchase or drink any competitor products or face termination from the company.

Coca-Cola once terminated Brazil footballer, $750 000 per year contract /endorsement deal after he was sighted with two cans of Pepsi in a live match. 

So all their foods, as a Coca-Cola worker you can't be caught eating any food or snacks made by Pepsi, same as Pepsi worker can't be caught eating any food or snacks made by Coca-Cola.