The Austrian Constitutional Court nullified a decision regarding the loss of the Austrian citizenship of a naturalised Austrian who allegedly had reacquired Turkish citizenship. The provincial citizenship office of Vienna had qualified an alleged extract from the Turkish electoral register as proof that the Austrian had again become a Turkish citizen. According to Austrian law the voluntary acquisition of a foreign citizenship provokes the automatic loss of Austrian citizenship. As a consequence the man, who had become Austrian more than twenty years ago in 1996, lost his Austrian citizenship ex lege at some unknown time between 1996 and 2017, the authority declared in its decision from December 2017. In the first instance the Administrative Court of Vienna confirmed this decision in August 2018; the Constitutional Court now found it in violation of the constitution.
The alleged extract from the Turkish electoral register, an electronic list of almost 100.000 names, is of unknown origin, has been leaked to political parties and passed on to the authorities last year. Since then several thousand proceedings have been started. In Vienna alone, almost 400 cases have been decided negatively, in 34 of them naturalised Austrians have already lost their Austrian citizenship.
In its verdict, the Constitutional Court found that the alleged extract from the Turkish electoral register does not qualify as legal evidence and further clarified that the burden of proof that someone acquired a foreign citizenship lies with the authority, not with the persons concerned.
As a consequence of the verdict, Vienna’s provincial government announced that it will immediately stop all proceedings in similar cases where the alleged extract from the Turkish electoral register has served as the sole evidence. Already decided cases should be reversed. In a first reaction Chancellor Sebastian Kurz (People’s Party, ÖVP) announced that the foreign minister will get into contact with Turkey to again start the exchange of information regarding the acquisition of nationality. Since 2010 Turkey does not share information on naturalisations any more. Vice Chancellor Heinz-Christian Strache (Freedom Party, FPÖ) demanded to stop further naturalisation of former Turkish nationals, although there is no legal basis for such a selective stop on naturalisations.
You can read the whole judgment (E 3717/2018-42) here: https://www.vfgh.gv.at/downloads/VfGH_Entscheidung_E_3717_2018_Doppelstaatsbuergerschaften.pdf (in German)