Employees across the massive U.S. Health and Human Services Department began receiving notices of dismissal Tuesday in an overhaul ultimately expected to lay off up to 10,000 people.

The cuts include researchers, scientists, doctors, support staff and senior leaders, leaving the federal government without many of the key experts who have long guided U.S. decisions on medical research, drug approvals and other issues.

At the National Institutes of Health, the world’s leading health and medical agency, the layoffs occurred as its new director, Dr. Jay Bhattacharya, began his first day of work.

“The revolution begins today!” Health Secretary Robert F. Kennedy Jr. wrote on social media as he celebrated the swearing-in of his latest hires: Bhattacharya and Martin Makary, the new Food and Drug Administration commissioner. Kennedy’s post came just hours after employees began receiving emailed layoff notices.

Kennedy announced a plan last week to remake the department, which, through its agencies, is responsible for tracking health trends and disease outbreaks, conducting and funding medical research, and monitoring the safety of food and medicine, as well as for administering health insurance programs for nearly half the country.

The plan would consolidate agencies that oversee billions of dollars for addiction services and community health centers under a new office called the Administration for a Healthy America.

The layoffs are expected to shrink HHS to 62,000 positions, lopping off nearly a quarter of its staff — 10,000 jobs through layoffs and another 10,000 workers who took early retirement and voluntary separation offers. Many of the jobs are based in the Washington area, but also in Atlanta, where the U.S. Centers for Disease Control and Prevention is based, and in smaller offices throughout the country.

HHS said the layoffs are expected to save $1.8 billion annually from the department’s $1.7 trillion budget, most of which is spent on Medicare and Medicaid health insurance coverage for millions of Americans.

Some staffers began getting lay off notices in their work inboxes at 5 a.m., while others found out their job had been eliminated after standing in long lines outside offices in Washington, Maryland and Atlanta to see if their badges still worked. Some gathered at local coffee shops and lunch spots after being turned away, finding out they had been eliminated after decades of service.

One wondered aloud if it was a cruel April Fools’ Day joke.

At the NIH, the cuts included at least four directors of the NIH’s 27 institutes and centers who were put on administrative leave, and nearly entire communications staffs were terminated, according to an agency senior leader, speaking on the condition of anonymity to avoid retribution.

An email viewed by The Associated Press shows some senior-level employees of the Bethesda, Maryland, campus who were placed on leave were offered a possible transfer to the Indian Health Service in locations including Alaska and given until the end of Wednesday to respond.

At the FDA, dozens of staffers who regulate drugs, food, medical devices and tobacco products received notices, including the entire office responsible for drafting new regulations for electronic cigarettes and other tobacco products. The notices came as the FDA’s tobacco chief was removed from his position. Elsewhere at the agency, more than a dozen press officers and communications supervisors were notified that their jobs would be eliminated.

“The FDA as we’ve known it is finished, with most of the leaders with institutional knowledge and a deep understanding of product development and safety no longer employed,” said former FDA Commissioner Robert Califf in an online post. Califf stepped down at the end of the Biden administration.