EXCLUSIVE: Sen. James Lankford, R-Okla., demanded Monday that DHS Secretary Alejandro Mayorkas clarify an apparent contradiction between his testimony that migrants failing to report to immigration officials is an "enforcement priority" and leaked ICE documents that suggest it is not.

In a letter obtained by Fox News, Lankford presses Mayorkas regarding an Immigration and Customs Enforcement initiative dubbed "Operation Horizon," in which authorities sent legal documents, including notices to appear in court, to 78,000 migrants who crossed the border without being processed for deportation. The migrants were initially given a "notice to appear" at an ICE facility within 60 days of their crossing.

Lankford asked Mayorkas to explain wording included in the documents, first reported by CBS News, which appeared to undercut the DHS secretary’s past testimony regarding migrants who failed to present themselves to immigration officials.

United States Secretary of Homeland Security Alejandro Mayorkas looks on during a conference as part of the High Level Security Dialogue at SRE Building on October 08, 2021 in Mexico City, Mexico.  (Photo by Hector Vivas/Getty Images) (Hector Vivas/Getty Images)

"We have discussed my concerns about this catch-and-release policy multiple times in HSGAC hearings, and you have previously testified that DHS considers individuals who do not report to be "an enforcement priority of ours," Lankford said.

"One of those documents reads: "Don’t worry if you are past the 60-day deadline to report from the time you entered the United States. Come in so you can help ensure the best outcome for your case." Another document reads: "Unless you have committed a serious crime, or the government thinks you may be a risk to the United States, YOU WILL NOT [emphasis in the original document] be taken into custody during the appointment," his letter added.

Lankford noted Mayorkas’ testimony during a Sept. 21 hearing with the Senate Committee on Homeland Security and Governmental Affairs. 

FILE PHOTO: A U.S. Customs and Border Protection agent monitors single-adult male detainees at Border Patrol station in McAllen, Texas, U.S. July 12, 2019.   (REUTERS/Veronica G. Cardenas//File Photo)

During the hearing, Lankford said there were more than 107,000 migrants who were released into the United States with "notices to report" for court proceedings. He pressed Mayorkas on whether DHS was acting against those who did not comply.

As of Sept. 10, of the 107,817 migrants who were released without formal notices to appear in court, 29,863 migrants or 28%, did not report to ICE as required, the Associated Press reported.

"Are we in pursuit of any of those individuals that did get a notice to report but then have not actually reported? Are those in the priorities? And have we actually picked up any of those folks for detention?" Lankford asked Mayorkas at the time.

"Senator, my understanding is of that figure; approximately 75 percent have indeed reported within the timeframe or within their reporting timeframe," Mayorkas said in response. "And as to those who have failed to report, that would qualify as an enforcement priority of ours."

Senator James Lankford speaks during a Senate Finance Committee hearing on the nomination of Chris Magnus to be the next U.S. Customs and Border Protection commissioner, in the Dirksen Senate Office Building on Capitol Hill in Washington, DC, U.S., October 19, 2021. Mandel Ngan/Pool via REUTERS

Border officials typically give migrants who attempt to cross the border a "notice to appear" in immigration court on a specific date for deportation proceedings. But with attempted border crossings at record highs in recent months, authorities shifted to issuing notices to report, which are faster to complete.

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Lankford asked Mayorkas to answer several questions about his testimony regarding the policy by Dec. 1, including details on how many migrants who received notices to appear or alternate documents have been detained, arrested or deported since March.

"If these individuals are an enforcement priority, why is ICE, a component of DHS that carries out the Department’s civil immigration enforcement priorities, telling migrants who have not reported in 60 days ‘YOU WILL NOT be taken into custody" and "Don’t worry if you are past the 60-day deadline?’" Lankford said.