(CNN) -- The Supreme Court will explore the limits of "speech crimes" in the Internet age, especially laws aimed at protecting those harassed or bullied online.
The justices will hear oral arguments this fall in the prosecution of Anthony Elonis over Facebook posts.
Some were expressed as rap lyrics, which Elonis said were "therapeutic" for dealing with emotional pain.
But the federal government alleges he crossed a line in May 2010 and used threatening language about his estranged wife and an FBI agent investigating him.
"Did you know that it's illegal for me to say I want to kill my wife?" Elonis wrote. "It's illegal. It's indirect criminal contempt. It's one of the only sentences that I'm not allowed to say."
The justices will decide the level of proof needed to convict someone for making criminal threats.
The issue in play here has broader implications for free speech amid the explosion of popular and often anonymous social media.
Key questions here involve whether sites like Twitter are in the same category as more conventional news links, and are general threats made online different than those made in person?
Elonis exhibited what the government called "troubling behavior" at his work, including allegedly starting to undress in front of a female co-worker.
He was fired for posting a Facebook picture from a Halloween-themed event, where Elonis is holding a knife next to that co-worker, as part of the staged activities. The online caption read: "I wish."
His online postings became more graphic, including one obtained by prosecutors in which Elonis wrote about his wife.
A court later granted a protection-from-abuse order filed by his spouse.
Other postings, by now being monitored by the FBI, were aimed at judges and law enforcement involved in the case. They also included a reference to school shootings.
Elonis was convicted in federal court and sentenced to 44 months in prison. He appealed.
The government told the high court that this was not a case of "careless talk, exaggeration, something said in a joking manner or an outburst of transitory anger. The statements that qualify as true threats (from the defendant) thus have a significant, serious character."
But Elonis' lawyers said the government did not prove his statements showed a "subjective intent to threaten," based on previous Supreme Court precedent. And they question whether "a reasonable person would regard the statement as threatening."
His lawyers said Elonis was simply exercising free-speech.
"Although the language was, as with popular rap songs addressing the same themes, sometimes violent, (the) petitioner posted explicit disclaimers in his profile explaining that his posts were 'fictitious lyrics,' they said.
"Art is about pushing limits. I'm willing to go to jail for my constitutional rights. Are you?" he asked at one point.
The court's docket has increasingly included constitutional disputes over the limits of digital and online technology. The justices are currently writing a ruling on whether police can obtain evidence of criminal activity from a suspect's cellphone without first obtaining a search warrant.