The American Civil Liberties Union has joined a legal fight over a Pennsylvania law it says silences convicts.

The law allows violent-crime victims to take legal action when they feel an offender's conduct is perpetuating the effect of the crime. The ACLU challenged it in federal court Thursday, saying it stifles advocacy and debate on prison issues.

Gov. Tom Corbett signed the law in October after Mumia Abu-Jamal made a recorded speech to a Vermont commencement.

Corbett says the state wanted to curb the "obscene celebrity" cultivated by convicts like Abu-Jamal, who is serving a life sentence for the 1981 killing of a Philadelphia police officer.

Abu-Jamal and prisoner-rights groups have also sued. He has drawn international support for claims he's the victim of a racist justice system.