President Donald Trump's administration began a mass firing of federal workers on 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 potentially 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.

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."