All Amazon warehouse workers must wear masks as of Aug. 9, whether or not they have been vaccinated against COVID-19, the company says. Previously, only unvaccinated employees had to wear masks.

The policy change announced Friday was made due to "the concerning spread of new COVID-19 variants in the U.S. and guidance from public health authorities and our own medical experts," Amazon spokesperson Kelly Nantel told CBS News. "We are monitoring the situation closely and will continue to follow local government guidance and work closely with leading medical health care professionals, gathering their advice and recommendations as we go forward to ensure our buildings are optimized for the safety of our teams," she added.

Amazon -- which has about 800,000 workers in the United States and is the nation's second-largest employer -- also announced last week that the date for its corporate workers to return to the office has been delayed from Labor Day to January 2022, CBS News reported.

Amazon is the latest of a number of major U.S. retail and grocery chains to change its mask policies as the United States grapples with a surge of COVID-19 cases fueled by the delta variant. Target now requires all store workers in counties that the U.S. Centers for Disease Control and Prevention says face a "substantial or high risk of transmission" to wear face coverings. The retailer, which has more than 1,900 stores across the country, also said it will continue recommending that customers wear masks in its locations but stopped short of requiring face coverings.