Jeffries Financial Group on Wednesday canceled all client parties and most travel plans globally, asking employees to work from home where possible due to a spate of COVID-19 cases.

The company has seen more than 40 cases since the start of December, Chief Executive Richard Handler said in a memo seen by Reuters, adding that the firm was re-imposing a mask mandate in all its offices, regardless of vaccination status.

The memo requested employees to work from home where possible and announced the cancellation of all travel except the most essential, unless pre-approved.

Jefferies is headquartered in New York and also has offices in Asia and Europe. The bank has felt the impact of COVID-19 particularly severely. Chief Financial Officer Peg Broadbent died due to coronavirus complications in March 2020.

More than 95% of Jefferies staff are now vaccinated, and all visitors to Jefferies' offices must be fully vaccinated, Handler said in the memo.

"That is why, with only a very few exceptions, most of our new cases have not required hospitalization," he said.

Jefferies' move raised questions about whether other banks will also review return-to-office plans, mask mandates and travel and entertainment policies.

U.S. banks have been more assertive than other industries in encouraging employees back to the office. Senior bankers such as Goldman Sachs Chief Executive David Solomon and Morgan Stanley Chief Executive James Gorman have spoken of the benefits of in-person interaction, particularly for younger employees.

Most major U.S. banks have been bringing staff back to the office since the summer. But those plans have come under renewed scrutiny due to the rapid spread of the Omicron variant.

So far, major U.S. banks have been sticking to their existing COVID-19 policies although sources at the "big six" firms say they are keeping a close watch on developments.

Jefferies, which the memo said had seen attendance average as high as 60% many days globally in recent weeks, said anyone who wants to enter a Jefferies office or event will have to have a booster vaccination administered by Jan. 31, unless they are not yet eligible to do so.