The Supreme Court has rejected an Illinois prosecutor's plea to allow enforcement of a law aimed at stopping 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 sets 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, 1 of the group's long-standing monitoring missions.

Opponents of the law say the right to record police is vital to guard against abuses.