The American Civil Liberties Union of Maryland has launched an ad campaign against the controversial Baltimore Police surveillance plane that began flying in April.

The campaign includes radio ads, print and digital ads in the Baltimore Afro-American newspaper, and digital billboards against the plane that collects video of wide swaths of the city. Supporters say the information could help police solve violent crimes.

But the ACLU and other critics have fought against the project, which has not been tested elsewhere.

They argue the surveillance is an invasion of privacy, unfairly targets minority neighborhoods that are already over-policed, and should not be operated by a police department still reeling from recent corruption scandals and operating under a consent decree with the U.S. Justice Department.

“In a majority Black city, the Baltimore City Police Department has once again found a way to target its residents and violate their rights,” Dana Vickers Shelley, executive director of the state ACLU, said in a statement.

“This invasive search into people’s constitutionally protected movements is an unprecedented attack on civil rights. This program never should have gotten off the ground, and we’re dedicated to ending it on behalf of the people of Baltimore.”

The ACLU is currently representing three plaintiffs in a federal lawsuit filed in April against the city, claiming the project violates residents’ constitutional rights. The ACLU unsuccessfully sought an injunction to prevent the launch, but a federal judge ruled that the program does not violate privacy rights of city residents and allowed the plane’s sixth-month trial run to proceed.

Police have said the plane will fly about 9,000 feet above the ground. But in recent days, data from Flightradar24.com, a site that displays flight tracking information including altitude, showed that the plane was hovering at 4,300 to 5,300 feet when the sky appeared generally clear. A police spokeswoman said the plane has lower altitude on cloudy days.

Some residents have complained about noise caused by the plane.

Critics have said the six-month pilot program, which is paid for through private donations, is the wrong approach to reducing the city’s violence.

“With numerous killings and countless stories of police brutality and excessive use of force against black people by officers with the BPD, it is bewildering that this department even entertains the notion that spy planes are an answer to end violence in Baltimore,” ACLU senior staff attorney David Rocah said in a statement.

“Instead of investing in black communities and effective, grassroots-based solutions to attack the root causes of violence, the city is jeopardizing the trust of residents with a military based tool that will be used to target black people, who are already over policed.”