In a statement issued on Wednesday, the HND called for action by the State Prosecutor's Office and the judiciary.
The HND complained about the inefficiency of courts in dealing with threats and assaults directed against reporters.
Reporter Marijan Malcevic was attacked while taking photos of the house of a family suspected of extortion.
According to Zagreb police spokeswoman Gordana Vulama, the reporter was attacked by the boyfriend of the 22-year-old daughter of the main suspect. The daughter is also suspected of extortion.