• Amazon on Friday informed warehouse workers they would be required to wear a mask inside operations facilities, regardless of their vaccination status, according to a notice viewed by CNBC.
• In May, Amazon told warehouse workers they could ditch their masks indoors if they were fully vaccinated.

Amazon is bringing back its mask mandate for warehouse workers amid a surge in Covid-19 cases due to the highly contagious delta variant.

Beginning on Monday, employees will be required to wear face coverings inside Amazon operations facilities — even if they're vaccinated — according to a notice sent Friday to employees, which was viewed by CNBC.

"We hope this will only be required for a few weeks," according to the notice, which was previously reported by Bloomberg. The new mask mandate applies to all U.S. Amazon sites, including where state and local guidance doesn't require face masks.

Amazon spokesperson Kelly Nantel confirmed the company is changing its mask policy in warehouses.

"In response to the concerning spread of new Covid-19 variants in the U.S. and guidance from public health authorities and our own medical experts, we are requiring face coverings indoors regardless of vaccination status," Nantel said in a statement, adding the company continues to monitor the situation closely to ensure its buildings are "optimized for the safety of our teams."

Previously, Amazon had been relaxing some of its coronavirus safety measures. In May, the company told warehouse workers they would no longer be required to wear a mask indoors if they were fully vaccinated. Last month, it began to wind down Covid testing in U.S. warehouses, The Information reported.

Amazon has not mandated vaccination among its employees, but it has nudged employees to get a coronavirus shot by offering them a bonus of up to $80. Additionally, it has told new hires that they will get $100 for showing proof of vaccination.

The company has also walked back its return-to-work guidance for corporate employees. Amazon said Thursday it was postponing a return to the office for its corporate employees until January 2022, following in the footsteps of other tech companies that have adjusted their guidance as the delta variant spreads rapidly across the globe.