The American Civil Liberties Union is asking federal agencies about the use of airplanes to monitor protests in Baltimore over the last week.
The ACLU filed Freedom of Information Act requests Wednesday with the FBI and other agencies seeking details about the flights of Cessna aircraft over Baltimore that the ACLU said were "indicative of surveillance activity."
The issue was first reported in The Washington Post.
Baltimore police regularly used helicopters to monitor protests throughout the city and broadcast instructions to protesters about implementation of a curfew and other issues. But privacy advocates say fixed-wing aircraft could potentially be used to conduct more sweeping surveillance on people who are not suspected of wrongdoing.
The FBI said Wednesday that it provided aircraft to Baltimore police for aerial imaging of potential criminal activity, not to monitor lawful protests.