"As our offices reopen, we will be requiring anyone coming to work at any of our U.S. campuses to be vaccinated," Facebook's VP of People Lori Goler said in a statement. "How we implement this policy will depend on local conditions and regulations."

According to Goller, Facebook will create processes for those who can't be vaccinated for medical or other reasons. The company will continue to evaluate its approach outside the U.S.

Facebook had already told full-time employees that most of them could continue working from home beyond the pandemic if their jobs could be done remotely.

The social media giant hasn't delayed its reopening plans for this fall, and a spokesman said that data would guide the social-media giant's decisions. Facebook has previously said it would likely open most of its U.S. offices at half capacity in September, and then fully in October.

"Expert guidelines state that vaccines are highly effective at preventing variants of COVID-19, including the delta variant," a Facebook spokesman said. "Our timelines to reopen our offices haven't changed." (Related: Facebook to force intellectual submission to coronavirus vaccines, promoting vaccine worship, not critical thinking or individual choice.)

Big Tech requires employees to get COVID-19 vaccine

Also on Wednesday, Google CEO Sundar Pichai told employees that the company would delay its return to office plans by one month, citing the fast-spreading delta variant. Pichai also said returning workers would have to be vaccinated.

Amazon also encouraged employees and contractors to be vaccinated. The company's current guidelines don't appear to require vaccination in order to return to its offices, though unvaccinated employees are required to wear masks. Face coverings are optional for those who have verification of being fully vaccinated.

Though employer-mandated vaccine requirements seemed rare just a few weeks ago, the rise of the delta variant and new guidance from the Centers for Disease Control and Prevention (CDC) seem to have played a role in shifting some executives' thinking.

On Tuesday, July 27, the CDC walked back its earlier mask guidance for fully vaccinated people, saying that they should again wear masks indoors in places with high transmission rates. CDC Director Rochelle Walensky said the change was due to new information on the delta variant, showing that some vaccinated people infected by the strain could still spread it to others.

The surge in COVID-19 cases is giving some companies and workers pause over looming return-to-office plans, even as a number of employers push ahead and reopen workplaces.

Delta variant looms over return-to-office-plans of corporate bosses

Many corporate bosses have been moving toward a significant return to corporate campuses after Labor Day. Others say they are feeling pressure to delay from employees who are voicing fresh concern about the spread of the highly transmissible delta variant and swaths of unvaccinated people.

Apple earlier told its workers that its back-to-the-office timeline would be delayed at least until October, according to a person familiar with the notice. The company also promised to give employees at least one month's notice before recalling them to an office.

The delta variant is the most contagious version of the virus to be identified. In weeks, it has become the most common strain in the U.S., accounting for 83 percent of analyzed infections.

Many companies remain cautious. In late June, food-services and facilities-management company Sodexo updated its mask guidance, recommending that all staffers continue to wear a mask, even if vaccinated.

Sodexo has kept many of its pandemic safeguards in place, such as physical barriers between tables in restaurants and the cafeterias it runs in corporate offices and on college campuses. Salad bars and self-serve buffets mostly remain closed.

With variants spreading, Sodexo is taking count of how many gloves, N95 masks, gowns and personal protective equipment it has in stock for workers.

"What I really worry about most is our ability to be agile and nimble," said Brigette Philpot, vice president of health, safety and environment for Sodexo North America. "Is delta the beginning of our never-ending journey to try to be effective with dealing with variants?"

Executives at Citigroup Inc. have said the company is letting data determine the bank's return-to-work plans. The company hasn't set an office return date, but said it expects to come back in September, although it will consider conditions at that time.

Some companies can't wait to have employees back at office

Even if companies aren't adjusting plans, some are talking with workers about the delta variant, aiming to address concerns. Terumo Blood and Cell Technologies, a medical device company that plans to bring 1,000 workers back to its office near Denver in August, said it would hold an all-hands session featuring some of the company's doctors to explain the variant and answer questions.

Many of Terumo's workers are vaccinated, and the company expects people to adopt hybrid work schedules where they are in the office two to three days a week, said Bon Lopez, senior vice president of human resources. If Colorado health officials or others add new restrictions that would affect in-office work, the company will comply and adjust its approach, he said.

Netflix Inc. Chairman and co-CEO Reed Hastings has made no secret about wanting to get the streaming giant's 9,000 employees back in the office. "Not being able to get together in person, particularly internationally, is a pure negative," Hastings said.

Netflix is encouraging its workers to return to the office at least part time after Labor Day, but keeping it voluntary, people familiar with the company's plans said.

Workers remain worried

Many workers remain worried. Miranda Doerfler, a 30-year-old poker dealer, was furloughed from her job at a casino near Boston early in the pandemic and her unemployment benefits run out in September. Though she's fully vaccinated and has been applying for other casino jobs, Doerfler said she has a weak immune system and is anxious about returning to a crowded indoor workplace.

"I'm still very nervous about the delta variant," she said. "Even being vaccinated, I'm very nervous about getting something that seems very aggressive, like the variant. I already have breathing troubles. I think I would do very poorly if I got sick."

Follow Pandemic.news for more news related to the coronavirus pandemic.

Sources include:

TechCrunch.com

CNBC.com

WSJ.com