Walmart announced Friday it is again requiring some American employees to wear face masks, while Disney mandated non-union US employees get vaccinated.

The moves come as US officials redouble efforts to encourage more vaccinations in response to the highly contagious Delta variant of Covid-19.

The world's largest retailer, Walmart said it will again require employees to wear face masks at stores in areas of the United States with high rates of Covid-19 transmission.

The chain, which has become something of a bellwether for safety protocols in the United States during the pandemic, said it would also post signs at stores to "strongly encourage" customers to wear masks or face coverings, the company said on its website.

The company cited revised guidance from the Centers for Disease Control and Prevention (CDC), which on Tuesday said vaccinated Americans in high-risk parts of the United States should resume wearing masks indoors, as infections caused by the Delta variant rise.

Walmart workers in areas of high transmission "are required to wear a mask or face covering while working indoors, regardless of vaccination status," the company said.

The policy will be set by region, following CDC analysis on transmission rates, the company added. The guidance will be updated each Monday when the CDC releases new data.

Walmart's July 2020 face mask requirement made such rules mainstream among retailers and throughout corporate America at a time when the virus was spreading quickly and there was little political consensus around masks.

The CDC in May lifted mask guidance for people who were fully vaccinated, and Walmart dropped the requirement for customers the following day. Many other companies soon followed.

Walmart's announcement comes as large businesses make similar moves as worries have risen over the Delta variant.

Later Friday, Disney announced its new vaccination requirement for non-union employees, adding it was in talks over extending the policy to union employees as well.

Covid-19 vaccinations provide "the best protection against severe infection, we are requiring that all salaried and non-union hourly employees in the US working at any of our sites be fully vaccinated," Disney said.

Disney announced earlier this week it was again requiring face masks in indoor spaces at its US theme parks.

More companies have also begun to require employees be vaccinated. On Wednesday, Google and Facebook said workers returning to offices will need to be vaccinated against Covid-19.

Twitter has also shifted policies, closing its New York and San Francisco offices and pausing additional reopenings, a spokesperson said.