More than 150,000 federal employees will leave the U.S. government payroll this week after accepting buyouts ¡ª the largest single-year exodus of civil servants in nearly 80 years, triggering what unions and governance experts warn is a damaging loss of institutional expertise.

The official resignations begin on Tuesday for workers who opted into a deferred exit program that kept them on the payroll through September. The buyouts are a cornerstone of President Donald Trump¡¯s push to shrink the federal workforce, combining financial incentives with threats of dismissal for those who declined the offer.

Many left their agencies months ago, according to the federal government¡¯s HR office, and have effectively been on paid leave.