Hundreds of Twitter employees refused on Thursday to sign a pledge to work “long hours at high intensity”, threatening the site’s ability to keep operating and prompting hurried debates among managers over who should be asked to return, current and former employees said.

The crisis came in response to an ultimatum the site’s new owner, Elon Musk, issued Wednesday demanding that employees sign a pledge to work harder by 5pm eastern time Thursday or accept three months’ severance pay, several media outlets reported.

As the deadline approached, hundreds of Twitter employees appeared to have decided to depart with the severance pay, the people said. Twitter later announced via email that it would close “our office buildings” and disable employee badge access until Monday, the New York Times reported.

Twitter, which has lost many of its communication team members, did not respond to a request for comment.

The departures include many engineers responsible for fixing bugs and preventing service outages, raising questions about the stability of the platform amid the loss of employees.

On Thursday evening, the version of the Twitter app used by employees began slowing down, according to one source familiar with the matter, who estimated that the public version of Twitter was at risk of breaking during the night.