Austria's Chancellor Sebastian Kurz said he is powerless to stop the upcoming gathering, The Local reported.
"The event taking place is an event organized by the (Croatian) Church," Kurz said ahead of the annual May 12 gathering in Bleiburg, a small town in the southern Austrian state of Carinthia, close to the Slovenian border.
"That means it is neither the decision of the federal government nor of the state premier (of Carinthia) and his administration whether this event takes place," he added.
They said that Ustasha symbols are banned in Croatia, but not in Austria, and called for a law at the EU level that would ban all Nazi and fascist symbols.
Austria's Documentation Center of Austrian Resistance (DOW) resistance archive center specializing in documenting Nazism and neo-Nazism, has called Bleiburg "the biggest fascist gathering in Europe."
The upcoming rally will remember the killing of sympathizers of Croatia's Ustasha regime and others at the hands of Yugoslav partisans in 1945 in and around Bleiburg.
According to various estimates, between a few hundred and tens of thousands Ustashas were killed.
The DOW, which deals with research concerning resistance and persecution from 1934 until 1945, exile, Nazi crimes and, right-wing extremism after 1945, has slammed the upcoming commemoration of the Bleiburg events as “the biggest fascist meeting in Europe."
During WWII, members of Croatia’s Ustasha government allied to Nazi Germany, killed tens of thousands of ethnic Serbs, Jews, Roma and Croatian antifascists at the Jasenovac death camp.
The Ustasha – Croatian Revolutionary Movement – was a fascist, racist and ultranationalist organization active, in its original form, between 1929 and 1945.
In April 1941, it was appointed to rule a part of Nazi-occupied Yugoslavia as the Independent State of Croatia, which has been described as both an Italian-German quasi-protectorate, and as a puppet state of Nazi Germany.