WASHINGTON — President Donald Trump’s administration began a mass firing of federal workers Thursday.

Office of Personnel Management officials met with agency leaders and advised them to dismiss probationary employees, according to a person familiar with the matter.

Hundreds of thousands of people could be affected, according to data from the Office of Personnel Management, although the exact number of people who will be terminated was not immediately clear.

Follow live politics coverage here.

Employees who have probationary status have typically been with the federal government for only one or two years — before all their civil service protections have kicked in.

“The probationary period is a continuation of the job application process, not an entitlement for permanent employment,” an OPM spokesperson said in a statement. “Agencies are taking independent action in light of the recent hiring freeze and in support of the President’s broader efforts to restructure and streamline the federal government to better serve the American people at the highest possible standard.”

The American Federation of Government Employees, a union for federal workers, condemned the move. AFGE President Everett Kelley said in a statement that the administration “has abused the probationary period to conduct a politically driven mass firing spree, targeting employees not because of performance, but because they were hired before Trump took office.”

“These firings are not about poor performance — there is no evidence these employees were anything but dedicated public servants. They are about power,” Kelley continued. “They are about gutting the federal government, silencing workers, and forcing agencies into submission to a radical agenda that prioritizes cronyism over competence.”

The exact extent of the firings is unclear. The Department of Veterans Affairs announced on Thursday that it was dismissing more than 1,000 employees, including certain probationary employees. The total number of probationary employees across the department is over 43,000, but the “vast majority” of the probationary employees “are exempt from today’s personnel actions because they serve in mission-critical positions — primarily those supporting benefits and services for VA beneficiaries — or are covered under a collective bargaining agreement,” the VA said in a press release.

The Education Department began terminating dozens of probationary employees on Wednesday. At the Department of Housing and Urban Development, senior-level managers were told in meetings who on their teams would be cut. They were also told to expect up to a 50% reduction in workforce at the housing agency, according to two HUD employees. The U.S. Forest Service is planning to terminate at least 3,400 people, according to Dennis Lapcewich, communications chair for the National Federation of Federal Employees’ Forest Service Council.

The move comes after an OPM spokesperson said Wednesday that about 75,000 federal employees accepted the White House’s “deferred resignation” offer to leave their roles but be paid through September. NBC News cannot independently verify the number.

In recent weeks, the Trump administration has taken aim at the U.S. Agency For International Development and the Consumer Financial Protection Bureau. Thousands of institutional support contractors at USAID were fired or placed on leave this month. 

Elon Musk’s Department of Government Efficiency has promised to slash what he and Trump paint as wasteful spending. 

On the first day of his second term, Trump declared a hiring freeze, meaning that vacant federal civilian positions could not be filled, nor could the government create new positions in most cases. The freeze has faced some legal challenges, with a federal appeals court on Tuesday rejecting the Trump administration’s bid to pause a lower court’s order that temporarily halted the federal funding freeze.