In-N-Out is barring staff from wearing masks unless they have a medical note. The burger icon wants customers to see employees' smiles.

• In-N-Out Burger is an iconic fast-food chain based in Southern California.
• The chain said workers must have a medical note to wear a mask in five states where it operates. 
• The chain said the new mask rule emphasizes the importance of showing customers associate smiles. 

In-N-Out, owned by billionaire Lynsi Snyder, is barring workers from wearing masks without a medical note in five states where it operates restaurants, according to an internal memo leaked on Twitter.