Jefferies Financial Group (JEF.N) on Wednesday cancelled all client parties and most travel, asking employees to work from home when possible due to a spate of COVID-19 cases.

The firm has had more than 40 new COVID-19 cases this month including 10 on Tuesday, Chief Executive Richard Handler said in a memo seen by Reuters. Handler added that Jefferies was re-imposing a mask mandate in all offices, regardless of vaccination status.

The investment bank, which has 3,000 employees worldwide, is headquartered in New York and also has offices in Asia and Europe. Staff returned to offices in October. The company has felt the pandemic’s impact acutely. 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.

Goldman Sachs (GS.N), Morgan Stanley (MS.N) and JPMorgan (JPM.N) have had most workers back at offices on a rotational basis since the summer.

Others, like Wells Fargo (WFC.N), Citigroup (C.N) and Bank of America (BAC.N), have taken a more flexible stance.

Wells Fargo pushed its return-to-office plans back to January 2022, while Citigroup employees in New York, Chicago, Boston, Philadelphia and Washington, D.C. have been working from the office at least two days a week since Sept. 13.

Major U.S. banks have also been continuing with holiday parties and client meetings since the Omicron variant was discovered, sources said, although they require proof of vaccination to attend.

In Europe, where Omicron has spread more rapidly, some banks have cancelled events such as JPMorgan’s annual festive carols reception in London and year-end party in Paris.

Deutsche Bank (DBKGn.DE) has told its London staff they can hold small gatherings at the team level. Asset manager Schroders (SDR.L) and the City of London Corporation, which runs London’s historic financial district, ask guests to take rapid tests before some festive events.

Some large U.S. companies are also pushing back their office-return date due to the Omicron variant.

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.