Google and Facebook said on Wednesday that all U.S. employees must get vaccinated to step into offices.
And Twitter says its shutting its reopened offices in the country, as the highly infectious Delta variant drives a resurgence in COVID-19 cases across the United States.
Twitter had started allowing employees back to its campuses in San Francisco and New York at 50% capacity about a fortnight ago after more than 16 months at home.
But the Delta variant, which first emerged in India, has spread quickly and now accounts for more than 80% of U.S. coronavirus cases.
San Francisco-based ride-hailing company Lyft, which had already made vaccinations mandatory for employees returning to the office, postponed its reopening from September to February.
Streaming giant Netflix has also implemented a policy mandating vaccinations for the cast and crew on all its U.S productions, according to a Deadline report.
Apple plans to restore its mask requirement policy at most of its U.S. retail stores, both for customers and staff, even if they are vaccinated, Bloomberg News reported.
Google also said on Wednesday it would extend its work-from-home policy through to Oct. 18 due to a recent rise in cases.
Many tech companies including Microsoft and Uber have said they expect employees to return to offices.