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.

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.

The new mask rule, confirmed by Insider in calls with the chain's customer service department, goes into effect in mid August — about four months after Biden officially ended the Covid national emergency.

"We are introducing new mask guidelines that emphasize the importance of customer service and the ability to show our associates' smiles and other facial features while considering the health and well-being of all individuals," said the memo, which was addressed to employees in Arizona, Colorado, Nevada, Texas, and Utah.

"No masks shall be worn in the store or support facility unless an associate has a valid medical note exempting him or her from this requirement," the memo said.

Employees must provide a valid medical note to a store manager, divisional manager, manager, or human resources, the memo said.

"Without disclosing the medical diagnosis or confidential medical information, the medical note should clearly state the reason for the exemption and include the estimated duration, if applicable," the memo said.

Employees who require a mask for medical reasons must wear a company-provided N-95 mask, according to the memo.

Failure to comply could lead to "disciplinary action up to and including termination of employment," the memo said.

Public health and science commentator Lucky Tran posted the memo on Twitter on July 14. The post generated more than 2.3 million views and nearly 3,000 retweets. A link to the memo was also posted on a Mailchimp archive associated with In-N-Out, which lists the company's email communications with employees.

Many people questioned the In-N-Out policy, with one person comparing it to prohibiting construction workers from wearing hard hats.

"How can an employer legally ban their employees from wearing an N-95 mask at work for their personal safety?" one person wrote. "That's like a construction company banning hard hats, high vis, or welding shield on building sites."

Mask advocacy group Mask Together America called In-N-Out's new policy "mask bullying." A Change.org petition, with nearly 1,000 signatures, was started to ask the chain to reverse its new mask policy. People also shared contact information for the company, and asked others to call and complain.

In-N-Out did not respond to requests for comment.

The chain, which is celebrating its 75th anniversary later this year, is known for its sparkling-clean restaurants and cheerful workers dressed in white aprons and paper hats. It was founded in 1948 by Snyder's grandparents, Harry and Esther Snyder. The Snyders believed in selling fresh, not frozen burgers, in a clean and friendly environment.

In-N-Out, which announced plans to expand to Tennessee earlier this year, also operates in California and Oregon. In those states, employers cannot ban employees from voluntarily wearing masks. In a separate memo posted to the Mailchimp archive, In-N-Out said associates in Oregon and California who "choose to wear a mask" must wear a company-provided N-95 mask.

Are you an In-N-Out insider with insight to share? Got a tip? Contact this reporter at 714-269-8873 or via email at nluna@insider.com