Citigroup is putting the brakes on plans to bring more of its roughly 201,000 employees back to their offices, saying that fewer than half will do so until there is an effective vaccine to prevent COVID-19.

“Unless there’s a vaccine, and while the virus is still around, the max we can get to is 30% or 40% in offices,” Paco Ybarra, CEO of Citi's Institutional Clients Group, said during a conference call, as reported by Bloomberg

More immediately, the company said it will postpone a return for employees in 13 states, including Florida and Texas, where coronavirus infections have been mounting, Banking Dive reports.

Previously, Citigroup had said that it believes in the importance of working in office space and that the bank wants all of its employees to return eventually. But one important difficulty Citigroup has faced in its efforts to return workers to urban office spaces is their reluctance to take public transportation during the pandemic, Ybarra said.

Citigroup isn't alone among major U.S. financial institutions whose reopening is going slowly. Bank of America let employees know recently that its goal for returning to office space is Labor Day, which is Sept. 7 this year, according to an internal memo cited by Bloomberg. Capital One and TD Bank are keeping employees home until September, Banking Dive reports.

Overall, returning any employees to large office buildings is proving problematic, even in places where the pandemic seems to be ebbing. After New York City allowed offices to reopen late in June, few workers actually went back to their offices.