A statement signed by vice president Zdenko Duka said that although the sentence was not final and was suspended, the HND was very dissatisfied because prison sentences were still being handed down for alleged libel in the press.
The statement read the HND advocated either completely decriminalising libel or not making it punishable by imprisonment if it remained a crime.
The statement recalled that Matvejevic was given a five-month prison sentence by the Zagreb Municipal Court on November 2 for libeling and offending writer Mile Pesorda in an article entitled "Our Taliban" which appeared in Jutarnji List daily four years ago.
In a statement published on their website on Friday, Reporters Without Borders said that even though Croatia had started EU entry negotiations, the Matvejevic case proved that Croatian law "still does not allow journalists to work freely without risk of prison".
The statement said this was the third time in the last 12 months that a journalist in Croatia was given a prison sentence for libel.
It added that if Croatia wanted to join the EU in 2007, it must change the press law at once.