The U.S. Internal Revenue Service is preparing to fire thousands of workers next week, a move that could squeeze resources at the tax-collecting agency during the critical tax-filing season, a person familiar with the matter said.

Officials from the Office of Personnel Management, which oversees federal hiring, ordered all agencies on Thursday to dismiss their probationary employees, who are newer to their positions and do not enjoy full civil service job protections.

It was unclear how many thousands of employees would be fired at the IRS, whose workforce totals about 100,000 people.

"They are trying to reduce numbers across the board with no analysis to the impact it will have on operations," the person familiar with the matter said, expressing concerns the cuts will hamper the agency's ability to weather tax-filing season.

News of the IRS workforce cuts was first reported by The New York Times.

The IRS did not immediately respond to a request for comment.