According to two Twitter sources (1)(2), access to Facebook has been blocked for employees of Vienna City Hall. Members of political parties may gain access again, but are at the moment also locked out of what bemused council member Marco Schreuder calls "an important comunications tool".
There is no official statement why this step that amounts to Internet censorship is deemed necessary. Obviously the city hall itself is not thinking about starting their own Facebook presence anytime soon.
Update: City hall representative says Facebook was not blocked, only access made more difficult to protect taxpayers' money (via ORF Futurezone).