Transit authorities in cities across the country are quietly installing microphone-enabled surveillance systems on public buses that would give them the ability to record and store private conversations, according to documents obtained by a news outlet.

The systems are being installed in San Francisco, Baltimore, and other cities with funding from the Department of Homeland Security in some cases, according to the Daily, which obtained copies of contracts, procurement requests, specs and other documents.

The use of the equipment raises serious questions about eavesdropping without a warrant, particularly since recordings of passengers could be obtained and used by law enforcement agencies.