The head of the Transportation Security Administration said on Thursday that "under 1,000" illegal immigrants have been allowed to board planes using warrants as identification this calendar year -- as he faced a grilling on the matter from Sen. Josh Hawley, R-Mo.

Hawley asked TSA Administrator David Pekoske at a Senate hearing about a TSA policy that allows illegal immigrants to use warrants, which represent civil immigration enforcement and are not criminal arrest warrants, as an alternative form of identification.

"How many individuals have presented TSA with arrest warrants or deportation notices and been allowed to travel this calendar year?" Hawley asked.

"Under 1,000 sir," Pekoske replied.

HAWLEY SEEKS ANSWERS ON ‘UNACCEPTABLE’ TSA POLICY OF ALLOWING ILLEGAL IMMIGRANTS TO USE WARRANTS AS ID 

Hawley had written to Pekoske earlier this year about the policy, which he called "unacceptable" but had not received a response. Pekoske said he would be receiving one on Friday.

"For noncitizens and non-U.S. nationals who do not otherwise have acceptable forms of ID for presentation at security checkpoints, TSA may also accept certain DHS-issued forms, including ICE Form I-200," a TSA spokesperson told Fox News earlier this year. That refers to a civil immigration arrest warrant.

The agency added that the document will then be validated via an "alien identification number" that involves personally identifiable information being checked against a number of Customs and Border Protection (CBP) databases, including the CBP One mobile application and TSA’s National Transportation Vetting Center (NTVC).

On Thursday, Pekoske said that the presentation of a warrant marked the beginning of a further verification process.

"These individuals who have these arrest warrants, these arrest warrants were issued by Border Patrol or a customs officer, and they serve as a beginning of our identity verification process so you can't walk up to a checkpoint, wave that form and then go right through into screening," he said.

SENATE REPUBLICANS QUIZ BIDEN ADMIN ON TSA ALLOWING ILLEGAL IMMIGRANTS TO USE WARRANTS AS ID 

While Pekoske said those use who warrants as ID also received enhanced screening, Hawley asked if they were given an in-person interview by a federal security director -- to which Pekoske said they were only interviewed by officers present at the checkpoint.

Josh Hawley

Sen. Josh Hawley, R-Mo., quizzed TSA Administrator David Pekoske on the policy. (Tom Williams/CQ-Roll Call, Inc via Getty Images)

Hawley pushed the TSA chief on why he would allow illegal immigrants with such a warrant onto a flight at all.

"We aren’t looking at whether a person is legal or illegal in the country," he said. "Our role is to make sure that people who may pose a risk to transportation that is significant enough to require enhanced screening or to not allow them to fly."

"So your position is someone who is known to have violated the laws of the United States does not thereby need enhanced screening?" Hawley said.

"Sir, there are people who violate the laws of the United States every day who fly," Pekoske responded. "We look for things related to transportation security."

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While Pekoske again stressed that the warrant is "the beginning of an identity verification process that follows" Hawley was not convinced.

"I think you’re going to have a hard time explaining to folks who wait for all of this time in these lines, who subject themselves voluntarily to the restrictions you impose…that you’re allowing illegal aliens with warrants for arrest to get on airplanes."

"I just find that totally extraordinary," he said.