The U.S. Supreme Court on Monday delivered another blow to a 50-year-old anti-eavesdropping law in Illinois, choosing to let stand a lower court finding that key parts of the hotly debated law run counter to constitutional protections of free speech.

In that critical lower-court ruling in May, the 7th U.S. Circuit Court of Appeals found that the law — one of the toughest of its kind in the country — violates the First Amendment when used against those who record police officers doing their jobs in public.

Civil libertarians say the ability to record helps guard against police abuse. The law's proponents, however, say it protects the privacy rights of officers and civilians, as well as ensures that those wielding recording devices don't interfere with urgent police work.

The Illinois Eavesdropping Act, enacted in 1961, makes it a felony for someone to produce an audio recording of a conversation unless all the parties involved agree. It sets a maximum punishment of 15 years in prison if a law enforcement officer is recorded.

As it drew the ire of civil liberties groups, state legislators endeavored to soften the law earlier this year, but those efforts stalled. The high-court's decision could prompt a renewed push to overhaul it.

But state Rep. Elaine Nekritz, a vocal opponent of the law, said court decisions hitting at its constitutionality could effectively nullify the most contentious aspects of the law and make further legislative action unnecessary.