The ACLU's New Jersey chapter is raising concerns about how NJ Transit monitors riders on its light-rail lines.

The civil liberties group says the agency is infringing on passenger privacy by not only capturing video on board its trains, but recording audio.

Another major concern, the ACLU says, is that NJ Transit has not disclosed what policies, if any, are in place to control who has access to the recordings, how they are used, how long they are kept, or how they are protected against unauthorized access.

"Are they simply creating a giant database?" asked Ed Barocas, legal director for the ACLU of New Jersey. "This has not been made public, and that is quite disturbing."

NJ Transit has defended the surveillance system, saying it needs to use available technology to keep riders safe in light of terrorism on mass-transit systems around the world.

Transit agencies commonly have video systems installed, but audio recordings are rare. Privacy advocates have also spoken out in a handful of other places where transit systems began recording audio of riders.

The video cameras were approved for River Line trains in October 2011, according to meeting minutes from the agency's governing board.

By the spring of 2013, cameras had been installed on the entire fleet of River Line trains. The system is being installed on the Hudson-Bergen and Newark light-rail lines as well.

Vehicles equipped with the cameras have signs alerting passengers to the video and audio recordings.

Though the cameras are noted in meeting minutes and other agency documents, no formal announcement of the recording system appears to have been made.

The ACLU began raising concerns after news reports this week highlighted the system.

"If they've been doing it that long and still haven't disclosed the policies . . . that's even more disturbing," Barocas said.

He said his group would push for the agency to stop recording audio, calling the measure "inappropriate and unnecessary," and to release its policies about the surveillance system.