U.S. investment bank Jefferies Financial Group has asked staff to work remotely until Jan. 31, according to an Instagram post on Monday from Chief Executive Officer Richard Handler.

The bank had called its staff back to offices in October, but was forced to return to work-from-home in December due to a spike in COVID-19 cases. It had also re-imposed a mask mandate in its offices, irrespective of vaccination status.

Handler also said the bank will not host indoor group events or other functions, and that it believes only "the most critical business travel" should occur.

As concerns over the Omicron variant of the coronavirus grow, Wall Street banks, which have been aggressive in bringing employees back to offices, have been forced to rethink their plans.

Goldman Sachs Group Inc also said on Sunday it was encouraging eligible U.S. staff to work from home until Jan. 18.