Citigroup will be the first major Wall Street institution to enforce a vaccine mandate by terminating noncompliant workers by the end of this month.

The bank reminded employees in a memo sent Friday about its policy, first disclosed in October, that they must be “fully vaccinated as a condition of employment.” At the time, the bank said that employees had to submit proof of vaccination by Jan. 14.

Those who haven’t complied by next week will be put on unpaid leave, with their last day of employment being Jan. 31, according to the memo, which was first reported by Bloomberg. A spokeswoman for the New York-based bank declined to comment.

Citigroup, the third biggest U.S. bank by assets and a major player in fixed income markets, has had the most aggressive vaccine policy among Wall Street firms. Rival banks including JPMorgan Chase and Goldman Sachs have so far stopped short of terminating unvaccinated employees.

Citigroup, led by CEO Jane Fraser since March of last year, said it made the decision because as a government contractor, it needed to comply with President Joe Biden’s executive order on vaccines. The bank also said that enforcing the mandate would help ensure the safety of employees who return to office work.

More than 90% of employees are compliant with the vaccine mandate, and that figure is rising as the deadline nears, according to a person with knowledge of the matter.

While some technology companies have embraced remote work as a permanent model, Wall Street CEOs including JPMorgan’s Jamie Dimon and Morgan Stanley’s James Gorman have been vocal about needing to pull workers back.

But the spread of the omicron variant of Covid-19 has forced companies to suspend back-to-work plans yet again, making it the latest disruption caused by the pandemic.

This story is developing. Please check back for updates.