(Philadelphia) -- The American Civil Liberties Union plans to appeal a recent federal court ruling that citizens can sometimes be stopped from recording police officers on duty.

The appeal concerns a ruling issued Friday in Philadelphia by U.S. District Court Judge Mark Kearney.

Kearney ruled that citizens don't have an unfettered right to record police activity. He said police are free to stop such recordings unless the person shooting the video announces he or she is recording as a challenge or protest to officers' actions.

ACLU attorney Mary Catherine Roper says the ruling reduces ``the ability of the public to monitor police activity.''

But the judge says the First Amendment doesn't give people a right to record police unless it is part of ``expressive conduct'' protected by the amendment.