The Atlanta-based agency’s leadership was notified of the decision Friday morning. The verbal notice came from the U.S. Department of Health and Human Services in a meeting with CDC leaders, according to a federal official who was at the meeting. The official was not authorized to discuss it and spoke to The Associated Press on condition of anonymity.

The affected employees are supposed to receive four weeks paid administrative leave, the official said, adding that it wasn’t clear when individual workers would receive notice.

HHS officials did not immediately respond to an emailed request for comment.

With a $9.2 billion core budget, the CDC is charged with protecting Americans from outbreaks and other public health threats. Before the cuts, the agency had about 13,000 employees, including more than 2,000 staff work in other countries.

Historically CDC has been seen as a global leader on disease control and a reliable source of health information, boasting some of the top experts in the world.

The staff is heavy with scientists — 60% have master’s degrees or doctorates. Most of the workforce does not belong to a union.

It’s not only new employees who are subject to probation. Probationary periods also are applied to veteran staffers who, for example, were recently promoted to a new job in management.

Dr. Joshua Barocas, an infectious diseases expert at the University of Colorado School of Medicine, said many of the probationary-status CDC employees are filling vital roles.

“It’s essentially assuming that they are not in a job that is crucial for the success of keeping everyone safe — just because they’ve been there for less than a year or less than six moths,” said Barocas, speaking Friday morning during an Infectious Diseases Society of America call with reporters.

“That sort of slash-and-burn approach is what will cause continued disruptions in our understanding of diseases” and disease outbreaks, he said.