In-N-Out Burger is prohibiting employees in five Western U.S. states from wearing masks unless they receive a medical note from a doctor.

The rules, which go into effect Aug. 14, apply to employees in Arizona, Colorado, Nevada, Texas and Utah.

The quick-serve chain is also mandating that employees in two other states, Oregon and California — the state with the most In-N-Out locations — only wear company-approved N95 masks if they choose to wear one.

The guidelines are designed to “emphasize the importance of customer service and the ability to show our Associates’ smiles and other facial features,” according to employee memos posted online.

Failure to comply with the new guidelines could lead to termination, the memo said.

In-N-Out did not respond to a request for comment.

Amid the Covid-19 pandemic, In-N-Out became a flashpoint when San Francisco officials ordered that city’s lone outlet for the chain to be closed in October 2021 after it failed to comply with a requirement that all restaurants check the vaccine cards of indoor diners. In-N-Out later preemptively closed all five of its locations in nearby Contra Costa County rather than comply with Covid rules there.

“We refuse to become the vaccination police for any government,” chief legal and business officer for In-N-Out, Arnie Wensinger, said in a statement at the time reported by the San Francisco Chronicle. “It is unreasonable, invasive, and unsafe to force our restaurant associates to segregate customers into those who may be served and those who may not, whether based on the documentation they carry, or any other reason.”

In-N-Out has been known for printing Bible verses on its food packaging. It drew attention in 2018 for donating to the California Republican Party, though Wensinger said the chain had historically given to both major political parties.