Austrian State Treaty from 1955:
PROHIBITION OF ANSCHLUSS
The Allied and Associated Powers declare that political or economic union between Austria and Germany is prohibited. Austria fully recognizes its responsibilities in this matter and shall not enter into political or economic union with Germany in any form whatsoever.
In order to prevent such union Austria shall not conclude any agreement with Germany, nor do any act, nor take any measures likely, directly or indirectly, to promote political or economic union with Germany, or to impair its territorial integrity or political or economic independence. Austria further undertakes to prevent within its territory any act likely, directly or indirectly, to promote such union and shall prevent the existence, resurgence and activities of any organizations having as their aim political or economic union with Germany, and pan-German propaganda in favor of union with Germany.
Now the question, is not the EU a political and economic union?