Apple Inc. warned retail employees about shortages of replacement iPhones, another sign the coronavirus outbreak is straining the company’s supply chain.

The company recently told technical support staff at stores that replacement iPhones for heavily damaged devices will be in short supply for as long as two to four weeks, according to Apple Store employees.

The workers, known as Geniuses, were advised in a memo that they can offer to mail replacement iPhones to customers and provide loaner devices to ease delays.

Some Apple stores have also noticed a shortage of individual parts, according to the employees, who asked not to be identified discussing private information. An Apple spokesman did not respond to requests for comment.

When a user brings in a damaged iPhone to an Apple store, the company can replaces individual parts such as the screen or camera. If the device is beyond repair, the company often provides a replacement phone rather than a brand new model.

The dearth of iPhone repair parts is one of the first visible effects from the virus on Apple’s operations. The company has begun to see shortages for the iPad Pro, Bloomberg News reported recently, while the supply of the iPhone 11 has begun to slightly tighten internationally. The Cupertino, California-based technology giant has also restricted employee travel to China, South Korea, and Italy, and has encouraged sick employees take leave. It’s also asking employees to have meetings virtually.

Apple is also rapidly re-opening its stores in China after being forced to temporarily shut all 42 of the locations due to the virus. The company has opened 38 stores as of Wednesday, according to a review of its retail website.