For a few glorious weeks, Wall Street employees who were vaccinated against Covid-19 could ditch their masks at the office.

That appears to be ending after the Centers for Disease Control and Prevention recommended this week that even fully vaccinated people should wear masks indoors in areas with significant transmission rates.

Citigroup told employees late Wednesday in a memo that they will now be required to wear masks in U.S. corporate offices, according to a person with knowledge of the situation. Other Wall Street firms including Morgan Stanley are closely monitoring the situation, said another person with knowledge.

The rise of the more contagious delta variant of Covid-19 has forced companies to reassess their plans to return employees to physical offices. Some, including Facebook, Alphabet and the Washington Post, are requiring employees to be vaccinated. Others such as Lyft have pushed back the date it expects employees back, saying it now expects them to return in February.

Citigroup, the third-biggest U.S. bank by assets, is following CDC guidance, according to the person who declined to be identified speaking of the company’s plans.

Back in May, the CDC said that fully vaccinated adults didn’t need to wear masks or socially distance indoors, and Citigroup had been following that protocol for corporate offices, although masks have been required at branch locations, the person said.

Employees sitting at their desks or eating in a cafeteria don’t need to wear masks, the person added. Citigroup declined to comment on the record about its employee policy, which was reported earlier by Bloomberg.

Financial firms have generally been more aggressive than other industries in touting a return to office life, based on concern that the collaborative culture of Wall Street banks was beginning to degrade during the remote work era.

JPMorgan Chase, the biggest U.S. bank by assets, had no changes as of Thursday from its latest guidance, which allowed the vaccinated to relinquish masks and daily health attestations as of this month, according to a person familiar with its planning.

Bank of America is maintaining its guidance that employees should use masks in areas where social distancing isn’t possible like elevators, said a person with knowledge of the bank. The firm still plans to bring back most of its employees after Labor Day, the person said.

This story is developing. Please check back for updates.