Citigroup Inc staff in the United States who have not been vaccinated against Covid-19 by January 14 will be placed on unpaid leave and fired at the end of the month unless they are granted an exemption, according to a company memo seen by Reuters on Friday.

The US bank announced its plan to impose new vaccination rules in October and now becomes the first major Wall Street institution to follow through with a strict vaccine mandate.

Its move comes as the financial industry grapples with how to bring workers back to offices safely and get back to business as usual at a time when the highly infectious Omicron coronavirus variant is spreading like wildfire.

Other major Wall Street banks, including Goldman Sachs & Co, Morgan Stanley and JPMorgan Chase & Co, have told some unvaccinated employees to work from home, but none has yet gone as far as sacking staff.

While Citigroup is the first Wall Street bank to enforce a vaccine mandate, a handful of other major US companies have introduced “no-jab, no-job” policies, including Google and United Airlines, with varying degrees of stringency.

More than 90 per cent of Citigroup employees have complied with the mandate so far and that figure is rising rapidly, according to a source familiar with the matter, adding that the timing of the vaccination mandate would be different for branch staff.

When it announced its policy, Citigroup also said it would assess exemptions on religious or medical grounds, or any other accommodation by state or local law, on a case-by-case basis.

The bank said then it was complying with the policy of US President Joe Biden’s administration requiring all workers supporting government contracts to be fully vaccinated, as the government was a “large and important” client.

“You are welcome to apply for other roles at Citi in the future as long as you are compliant with Citi’s vaccination policy,” the bank said in the memo. “If you are not vaccinated, we urge you to get vaccinated as soon as possible.”

Vaccination has become a divisive issue in the US with some people fiercely opposed and many Republicans critical of mandates imposed by governments and businesses.