The Supreme Court has rejected an appeal from the Cook County state's attorney to allow enforcement of a law prohibiting people from recording police officers on the job.
The justices on Monday left in place a lower court ruling that found that the state's anti-eavesdropping law violates free speech rights when used against people who tape law enforcement officers.
The law set out a maximum prison term of 15 years.
The American Civil Liberties Union filed a lawsuit in 2010 against Cook County State's Attorney Anita Alvarez to block prosecution of ACLU staff for recording police officers performing their duties in public places, one of the group's long-standing monitoring missions.
Opponents of the law say the right to record police is vital to guard against abuses.
Last May, a federal appeals court in Chicago ruled that the law "likely violates" the First Amendment and ordered that authorities be banned from enforcing it.
The appeals court agreed with the ACLU that the "Illinois eavesdropping statute restricts far more speech than necessary to protect legitimate privacy interests."
The appeals court ruling came weeks before the NATO summit when thousands of people armed with smart phones and video cameras demonstrated in the city. Officials had already announced that they would not enforce the law against summit protesters.
Public debate over the law had been simmering since last summer.
In August of 2011, a Cook County jury acquitted a woman who had been charged with recording Chicago police internal affairs investigators she believed were trying to dissuade her from filing a sexual harassment complaint against a patrol officer.
Judges in Cook and Crawford counties later declared the law unconstitutional, and the McLean County state's attorney cited flaws in the law when he dropped charges this past February against a man accused of recording an officer during a traffic stop.
Harvey Grossman, legal director of the ACLU of Illinois, said the organization was "pleased that the Supreme Court has refused to take this appeal. . .The ACLU of Illinois continues to believe that in order to make the rights of free expression and petition effective, individuals and organizations must be able to freely gather and record information about the conduct of government and their agents - especially the police. The advent and widespread accessibility of new technologies make the recording and dissemination of pictures and sound inexpensive, efficient and easy to accomplish."
The Associated Press contributed