As Americans pack their bags for holiday travel, a new report is raising key questions about a pilot program that scans the faces of international travelers.

The report criticizes the scope and execution of the program

The report, from Georgetown Law’s Center on Privacy and Technology, criticizes the scope and execution of Homeland Security’s biometric exit pilot program. The program, currently running at nine airports around the country, uses facial recognition technology to identify passengers leaving on international flights. Homeland Security says the program, which it plans to expand, can catch travelers fraudulently using another person’s personal documents.

But the report questions whether Homeland Security is vested with the power to build a program that scans Americans’ faces without approval from Congress, and says the program “stands on shaky legal ground.” The report says the agency also failed to follow proper federal procedures when creating the program.

The report also questions whether Homeland Security is correctly measuring the effectiveness of the program. The agency, according to the report, is hoping the program accurately accepts 96 percent of travelers with proper documentation, but it’s unclear how accurately the program can catch travelers attempting to leave with the wrong documents. The report also notes that facial recognition systems have frequently been shown to have biases against certain groups of people, and it’s unclear whether the biometric system is prone to flagging people based on their race or gender.

In response to the report, Sen. Edward Markey and Rep. Mike Lee have sent a letter to Homeland Security requesting more information and data on the program. “[P]otential flaws with this biometric technology raise a number of questions, especially since no perfectly accurate biometric scanning program currently exists,” the lawmakers write.