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The program was used on 873 passengers and 289 employees in the first two weeks of operation. The TSA said it will evaluate the results at the end of the test in April and decide on “future plans.”

Mr. Thompson said the original behavior program was sold to Congress as a way to speed up lines by clearing passengers and putting them through expedited screening.

Mr. Pistole told Congress last year that axing the program would mean longer lines.

“Defunding the program is not the answer,” he said. “If we did that, if Congress did that, what I can envision is, there would be fewer passengers going through expedited screening, there would be increased pat-downs, there would be longer lines and there would be more frustration by the traveling public.”

In their letter Thursday, the lawmakers said Mr. Pistole last year indicated that the behavior program was being used only “for exclusion purposes.”

“Given the lack of scientific validation that [behavior detection officers] are capable of detecting the presence of an individual who poses a threat to aviation security, it is unlikely that scientific validation exists to show that the use of the same methodology would enable BDOs to identify an individual who is a low risk and only requires minimal and expedited checkpoint screening,” they said.

In addition to Mr. Thompson, the letter was signed by Rep. John Conyers Jr. of Michigan, the ranking Democrat on the Judiciary Committee; Rep. Elijah E. Cummings of Maryland, the ranking Democrat on the Oversight and Government Reform Committee; and Rep. Cedric L. Richmond of Louisiana, the ranking Democrat on the Homeland Security transportation subcommittee.