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.

Those cuts are especially concerning because the positions typically require high-level security clearances and training that can take 18 months or longer, said Jill Hruby, who served as the NNSA administrator during the Biden administration. 

“These people are likely never going to come back and work for the government,” Hruby said in a phone interview. “We’ve had a very active program requiring an increase to our staff so the indiscriminate layoffs of people will be really difficult for the coming years.”

The firings — part of a wave of terminations across the federal government this week spurred by Elon Musk’s Department of Government Efficiency — underscore the chaos as the world’s richest man seeks to quickly overhaul the federal bureaucracy in Trump’s image. At the Small Business Administration earlier this week, some workers who were told they were being fired, received a second message telling them that they weren’t being terminated and that their jobs were safe — only to receive a third message telling them they were, in fact, out of a job.

The NNSA firings were part of a wider swath of dismissals across the Energy Department, which included employees at the Loan Programs Office, a recently formed unit to fund clean energy projects, the group responsible for preventing cyberattacks against the power grid, and the department’s general counsel office.

The Energy Department and the NNSA did not respond to requests for comment.

Nuclear Programs

The NNSA is a semi-autonomous arm of the Energy Department  responsible for producing and dismantling nuclear weapons, providing the Navy with nuclear reactors for submarines and responding to radiological emergencies, among other duties. 

The agency also plays a role a key role in counter-terrorism, transporting nuclear weapons around the country and responding to nuclear incidents around the world. Recent focuses have included examining how AI can be used to make it potentially easer for people to make nuclear bombs, Hruby said.

“These are areas where we’ve been concerned and staffed up to respond to that,” Hruby said. “These are working with high skill-levels that are willing to work around-the-clock if needed.” 

Among the deepest cuts was to the Energy Department’s Office of Clean Energy Demonstrations, where roughly 25% of its staff was eliminated, according to a breakdown of the cuts seen by Bloomberg News. That office received some $27 billion in funding from the Inflation Reduction Act, as well as bipartisan infrastructure law, to finance carbon capture, hydrogen and advanced nuclear projects. Among it’s priorities is managing an $8 billion plan to establish a network of hydrogen hubs throughout the US. 

“This program helps bring competitive manufacturing back to American shores, so weakening it is only going to help foreign competitors,” said Steven Nadel, executive director of the American Council for an Energy-Efficient Economy, a nonprofit group that advocated for the funding. 

Other cuts included roughly 50 people from the Energy Department’s Loan Programs Office, according to a person familiar with the matter. The green bank swelled to $400 billion in lending authority under President Joe Biden and has funded loans to companies including Rivian Automotive Inc. and California utility PG&E Corp. for a host of clean-energy projects. The program, which was among those frozen amid an ongoing review of Energy Department funding by the Trump administration, has nearly $47 billion in conditional commitments to companies it has yet to finalize. 

Read more from Fortune
–UnitedHealth falls after U.S. opens probe of Medicare billing
–Her 12-year-old son has autism and epilepsy and was kicked out of class.
–NYC’s most elite private high schools will cost nearly $70,000 this fall
–Tesla recalls more than 375,000 vehicles due to power steering issue
–Nissan shares surge on report Japan group may seek Tesla deal

Read more: GOP Targets Biden’s $400 Billion Clean-Energy Loan Program 

In addition, according to the breakdown, cuts included roughly a dozen people from Energy Department’s General Council’s office and approximately 20 individuals in its Grid Deployment Office, overseeing some $22 billion in federal funding for power grid projects. In addition, about 15 people in the Office of Manufacturing and Energy Supply Chains and about half a dozen from the Office of Cybersecurity, Energy Security, and Emergency Response, which guards against threats to the power grid and other energy infrastructure, were dismissed. 

In addition roughly 10% of the Energy Department’s information technology team was eliminated as well, according to a person familiar with the matter.