Zeljko Strize told reporters that the family of the arrested general and his attorneys, with whom he was in touch, supported the protest rally.
Strize said that the rally, to be addressed by retired generals, scholars, leaders of war veterans associations and Gotovina's attorneys, would pool more people than the 2001 rally for General Mirko Norac.
Politicians will not address the rally, Strize said, adding that the rally would be addressed by Admiral Davor Domazet Loso and General Ljubo Cesic Rojs.
Strize said the organisers of the rally would play recordings of speeches given by Prime Minister Ivo Sanader and other politicians at the meeting for Mirko Norac "to compare what they were saying then, and what they are saying now".
Participants in the meeting will send concrete requests to Croatian authorities regarding the arrest of General Gotovina, including the request that he be handed over to Croatian authorities and enter his plea in his country.
Strize called Gotovina's arrest an act of treason by Croatian authorities in relation to all soldiers, the families of soldiers killed in the war, war invalids, and the entire Croatian people.
Gotovina is the only indictee of the Hague war crimes tribunal whom the government prevented from being interviewed by investigators of the Hague tribunal, Strize said, adding that the government also failed to provide his attorneys with the necessary documents.