In-N-Out Burger, a popular fast food chain, will soon ban its employees in five states from wearing masks, emphasizing the "importance of customer service," according to a new policy.

Starting Aug. 14, In-N-Out employees in those states who want to wear a mask must have a valid medical note "exempting him or her from this requirement," a company memo says. Those who wear masks for medical reasons must wear a company-provided N95 mask, it says.

The new policy will apply to the chain's employees in Arizona, Colorado, Nevada, Texas and Utah.

"Our goal is to continue to provide safe and customer-centric Store and Support environments that balance two things that In-N-Out is known for — exceptional customer service and unmatched standards for health, safety, and quality," the memo says.

Those who fail to comply with the new guidelines could possibly be fired.

"We believe this policy will also help to promote clear and effective communication both with our Customers and among our Associates," the memo says.

The company said employees in Oregon and California locations who choose to or are required to wear a mask must wear a company-provided N95 mask. (The company did not go into detail about wearing a company-issued N95 mask versus one purchased by the employee.)

In-N-Out did not immediately respond to NPR's request for comment on the new policy.

However, chain's memo says the policy will be reviewed periodically to "ensure its effectiveness and compliance" with evolving health guidelines.

Following the news of its new mask policy, many across social media fired back at the fast food chain's announcement.

Dr. Judy Stone, an infectious disease physician, criticized the new policy, saying in a tweet that it violates the Centers for Disease Control and Prevention's COVID-19 recommendations and she urged followers to contact In-N-Out's corporate headquarters.

In a tweet, Holly Mancuso called it "a terrible policy," adding: "Respect your workers enough to let them make their own choices for their health."

In-N-Out is no stranger to being under fire for pushing back against COVID-19 policies.

In 2021, its San Francisco location was temporarily shut down by the Department of Public Health for not properly checking customers' proof of vaccination.

The Department of Health told NPR that public health officials had informed In-N-Out several times about the proof-of-vaccination requirement but that the restaurant did not comply.

An In-N-Out restaurant in Pleasant Hill, Calif., was also shut down for refusing to comply with county COVID protocols.

Arnie Wensinger, In-N-Out's chief legal and business officer, said in a statement at the time that the San Francisco restaurant posted signage to inform customers of the local vaccination requirements, but did not prevent those who didn't have the proper documentation from entering.

"We fiercely disagree with any government dictate that forces a private company to discriminate against customers who choose to patronize their business," Wensinger said. "This is [a] clear governmental overreach and is intrusive, improper, and offensive."

NPR's Rachel Treisman contributed to this report.