The FBI has engaged in "political policing," the ACLU said, including spying on peaceful activists. That raised the potential for abuse against innocent targets. The agency also claimed that it didn't need to demonstrate probable cause to use facial recognition, and couldn't confirm if it honored "constitutional obligations" to inform defendants in criminal cases when the tech was involved. And these concerns assume the systems are accurate, which they sometimes aren't -- the ACLU referred to studies showing racial and gender biases in facial recognition.

This isn't the first time the ACLU has pressed for disclosure. It filed Freedom of Information Act requests with the FBI and DEA in January. Both agencies recognized the requests, but didn't provide any "responsive documents," the ACLU said.

However the agencies respond to the lawsuit, they'll be swept up in a mounting opposition to unfettered use of facial recognition. California and the city of San Francisco recently passed measures banning key government uses of facial recognition, and companies like Facebook have shied away from past uses. There's an increasing sense that the privacy risks are too great to ignore, and that there should be at least some baseline restrictions on when facial recognition comes into play.