The Biden administration is set to introduce stricter testing for both vaccinated and unvaccinated legal travelers entering the United States amid the rising threat of the Omicron variant even while illegal migrants have gone mostly untested.

President Biden's enhanced winter COVID-19 strategy that will be announced Thursday will require every traveler entering the country, including returning U.S. citizens, to be tested one day before boarding their flight, according to the CDC. The rule will also apply to vaccinated travelers, who previously were only required to show a negative test no more than three days before their flight.

President Joe Biden

President Joe Biden. (AP Photo/Carolyn Kaster)

But the Biden administration has refused to put similar requirements in place for those who illegally cross the border, claiming in September that such individuals do not intend "to stay here for a lengthy period of time."

BIDEN'S VACCINATION MANDATE DOESN'T INCLUDE ILLEGAL IMMIGRANTS

"As individuals come across the border, and they are both assessed for whether they have any symptoms, if they have symptoms they are," White House press secretary Jen Psaki said at the time.

"The intention is for them to be quarantined," she added. "That is our process, they’re not intending to stay here for a lengthy period of time. I don’t think it’s the same thing. It’s not the same thing."

Jen Psaki speaks to media at White House daily briefing

White House Press Secretary Jen Psaki. (Photo by Drew Angerer/Getty Images)

As part of the enhanced strategy to fight the Omicron variant, the White House is considering a policy that would require travelers to take an additional test three to five days after they enter the country. More controversially, the administration is considering requiring all travelers to self-quarantine for seven days even if they receive a negative test. U.S. citizens would also be subject to this requirement, with fines and penalties for those who fail to comply.

Federal authorities say more than 200,000 people arrived in the country by plane every day in November so far, a number that does not yet include the Thanksgiving holiday. Health officials stressed that even if a quarter of those travels complied with the updated regulations, it could help scientists isolate thousands of infected individuals who could spread the virus.

But there is no indication the administration is rethinking its stance on testing illegal migrants who cross the border, despite border officials encountering 164,303 individuals at the border in October, the most recent month for which data is available. That number does not include "gotaways," the number of individuals who were able to sneak across the border without being arrested. The U.S. Border Patrol estimates more than 400,000 such individuals have illegally entered the country in the last 12 months.

President Joe Biden. REUTERS/Evelyn Hockstein

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Almost 12,000 border patrol employees have tested positive for COVID-19 since the pandemic began, with 51 having died from the virus.

The White House did not immediately respond to a Fox News request for comment.