The Trump administration reinstated on Tuesday hundreds of employees of the Centers for Disease Control and Prevention who had been placed on administrative leave in April.

The employees are all staff members of the National Institute for Occupational Safety and Health, a C.D.C. unit charged with preventing work-related injuries.

“This moment belongs to every single person who refused to stay silent,” said Micah Niemeier-Walsh, an industrial hygienist at NIOSH and the vice president of an American Federation of Government Employees union local that represents C.D.C. employees.

Last April, as part of the Health Department’s overhaul, Secretary Robert F. Kennedy Jr. cut about 2,400 positions from the C.D.C. He placed about 90 percent of the roughly 1,000 employees of NIOSH on administrative leave, with layoffs set to become effective that June.

But a court order in late May halted the terminations, leaving the workers in limbo. Separately, pressure from some members of Congress led to the reinstatement of about 328 NIOSH employees, including those who provided services to survivors of the 9/11 terrorist attacks.