The Energy Department is seeking to bring back nuclear energy specialists after abruptly telling hundreds of workers that their jobs were eliminated, according to two people familiar with the matter.

The employees, responsible for designing and maintaining the nation’s cache of nuclear weapons at the National Nuclear Safety Administration, were part of a larger wave of workers dismissed from the Energy Department, drawing alarm from national security experts. Between 300 and 400 NNSA workers were terminated, according to a person familiar with the matter.

The agency’s quick reversal was announced Friday in an all-staff meeting. The NNSA is seeking to recall the workers because they deal with sensitive national security secrets, according to the people, who weren’t authorized to talk about the matter, which is not public.