Google is postponing a return to the office for most workers until mid-October and rolling out a policy that will eventually require everyone to be vaccinated once its sprawling campuses are fully reopened.

The more highly contagious delta variant of the coronavirus is driving a dramatic spike in COVID-19 cases and hospitalizations. Google’s Wednesday announcement was shortly followed by Facebook, which also said it will make vaccines mandatory for U.S. employees who work in offices. Exceptions will be made for medical and other reasons.

In an email sent to Google’s more than 130,000 employees worldwide, CEO Sundar Pichai said the company is now aiming to have most of its workforce back to its offices beginning Oct. 18 instead of its previous target date of Sept. 1.

The decision also affects tens of thousands of contractors who Google intends to continue to pay while access to its campuses remains limited.

Even before the World Health Organization declared a pandemic in March 2020, Google, Apple and many other prominent tech firms had been telling their employees to work from home. This marks the third time Google has pushed back the date for fully reopening its offices.

Google’s vaccine requirement also could embolden other employers to issue similar mandates to guard against outbreaks and minimize the need to wear masks in the office.

While most companies are planning to bring back their workers at least a few days a week, others in the tech industry have decided to let employees do their jobs from remote locations permanently.