WASHINGTON — Thousands of intelligence officers could soon be fired for failing to comply with the government’s vaccine mandate, leading some lawmakers to raise concerns about national security.

At least 20% of employees at several agencies were not vaccinated against COVID- 19 as of late October, said Rep. Chris Stewart (R-Utah) of the House Intelligence Committee. At some of the 18 intelligence agencies, up to 40% were unvaccinated, Stewart said, citing information from the Biden administration. He declined to identify the agencies because data on vaccination rates are classified.

While many employees may get vaccinated before the Nov. 22 deadline for civilian workers, resistance to the mandate could leave agencies short on personnel. Intelligence officers are particularly hard to replace because of their specialized skills and the need for security clearance checks.

The Office of the Director of National Intelligence has declined to disclose vaccination rates in the intelligence community or what contingency plans might be in place in case of mass firings.

Director of National Intelligence Avril Haines declined at a hearing last week to disclose vaccination rates, but said officials “are not anticipating that it is going to be an issue for mission.” There are about 100,000 people in the intelligence community.

Stewart called on the Biden administration to approve more exemptions on medical, religious and other grounds, and to delay firing intelligence officers.

“What’s the impact on national security if we do that?” Stewart said. “You’re potentially firing thousands of people on the same day. And it’s not like you put an ad on Craigslist and have people apply by Thursday.”

President Biden has mandated vaccinations for federal employees, contractors and healthcare workers. The White House credits mandates with reducing deaths from a pandemic that has killed about 754,000 in the U.S. and more than 5 million worldwide.

Federal regulators and independent health experts have certified three COVID-19 vaccines as safe. A Centers for Disease Control and Prevention study found that from April to July, unvaccinated people were 10 times more likely to be hospitalized and 11 times more likely to die of COVID-19.

Vaccine mandates face significant resistance in an already tight market for businesses looking to hire. Some first responders and unions have resisted the mandates, saying they impinge on personal freedom.

House Intelligence Committee Democrats say they are confident the mandate will not harm the intelligence community.

Rep. Jason Crow (D-Colo.) said that the agencies were doing “quite well” and that vaccinations were part of employee readiness.

“If somebody is not willing to do what’s necessary to protect their own health and the health of their unit, that actually calls into question their ability to effectively do the job,” he said in an interview.

Federal employees who aren’t vaccinated or given an exemption by Nov. 22 could be suspended for up to 14 days, followed by possible dismissal.

The General Services Administration has advised agencies that “unique operational needs of agencies and the circumstances affecting a particular employee may warrant departure from these guidelines.”