An internal memo, obtained by CNBC, told staff that they must upload documents proving vaccination status.
Those who did not would be placed on unpaid leave and later sacked, it said.
Google has been pushing for an eventual return to the office - which has been repeatedly delayed - and expects those attending buildings to be vaccinated.
When contacted by the BBC, Google did not deny the accuracy of the US news channel's report on the leaked internal memo.
A spokesperson said: "As we've stated before, our vaccination requirements are one of the most important ways we can keep our workforce safe and keep our services running.
"We're committed to doing everything possible to help our employees who can get vaccinated do so, and firmly stand behind our vaccination policy."
CNBC's report said the memo, sent earlier this year, told employees they had until 3 December to send Google proof of vaccination or to apply for an exemption on medical or religious grounds.