Google and Facebook will require U.S. employees to be vaccinated against the coronavirus before returning to the company's offices, the tech giants said on Wednesday.

In a blog post, Google CEO Sundar Pichai said the vaccine mandate would apply to its U.S. offices in the coming weeks and would be required eventually for other locations.

"Getting vaccinated is one of the most important ways to keep ourselves and our communities healthy in the months ahead," Pichai wrote.

Shortly after Google's announcement, Facebook said it too will require anyone coming to work at its U.S. offices to be vaccinated.

"How we implement this policy will depend on local conditions and regulations. We will have a process for those who cannot be vaccinated for medical or other reasons and will be evaluating our approach in other regions as the situation evolves," Lori Goler, Facebook's vice president of people, wrote in a statement.

The tech giants' vaccine requirements could push other employers to follow suit.

So far, other major tech companies, including Apple and Amazon, have declined to mandate vaccines. Microsoft, in a note to employees, said it will not require vaccination to enter workplaces, but top company officials recommend employees receive the shot.

Pichai also said Google would push back the return-to-office date for most of its 144,000 employees from September to mid-October as the delta variant of the coronavirus spreads. Other tech companies have announced similar delays.

In his blog post Wednesday, Google's Pichai said he has been encouraged to see "very high vaccination rates" among Googlers.

"This is a big reason why we felt comfortable opening some of our offices to employees who wanted to return early," he wrote.

As the pandemic took hold last year, the tech industry was one of the first to send employees home to work. Now it's struggling with how and when to bring them back to the office, and to what degree it should let its vast workforce continue working remotely. Many companies have developed hybrid models, offering workers at least some flexibility.

Apple also has pushed back its return-to-the-office date to October, but the company said it is committed to having most employees work on location at least three days a week.

Microsoft is aiming for a September reopening of its offices. The company said the pandemic has led it to expand its hybrid work opportunities for workers.

Facebook is on track to reopen its offices in October but will allow employees to continue working remotely with permission. Facebook CEO Mark Zuckerberg has said he expects half of the tech giant's 48,000 employees to be working remotely in the coming years.

For Amazon workers, a return to the office is also slated for this fall. Amazon has said it will allow employees to work from home two days a week. A company spokesman declined to comment on whether it will issue a vaccine mandate.

Twitter is requiring its returning workers to show proof of vaccination before coming back to the office. Yet it has among the boldest remote work policies in the industry. The company announced in May that its employees can work remotely permanently if they so choose. Twitter Chief Financial Officer Ned Segal said in a tweet this month: "We aren't asking everyone to return. Ever," adding that Twitter staffers can do their work "on their sofa or in an office."

On Wednesday, Twitter announced it is shutting down its reopened offices in San Francisco and New York in light of updated guidelines from the Centers for Disease Control and Prevention.

Business software maker Salesforce has begun to bring employees back to its locations and the company is requiring its workers be vaccinated before returning, according to a company spokeswoman.

Editor's note: Google, Facebook, Apple, Amazon and Microsoft are among NPR's financial supporters