A Twitter account reportedly posted pictures of Leddy's Minnesota driver's license and a credit card. It also reportedly made violent threats against him.
"We alerted local and federal authorities immediately, as well as the NHL," an Islanders spokesperson said. "They're investigating the matter. Nick and his family are safe."
Newsday reported that the team's security director contacted the Nassau County, N.Y., police department and the FBI after threats were made against Leddy on Tuesday.
Leddy had been harassed for months on the now-suspended Twitter account.
Leddy, 24, was traded to the Islanders from the Chicago Blackhawks on Oct. 4 and signed a seven-year, $38.5 million contract extension last month.
He has 10 goals and 19 assists in 70 games this season for the Islanders, who are fourth in the Eastern Conference with 93 points.
- Scooby Axson